US2806923A - Thermostat - Google Patents

Description

Sept. 17, 1957 H. W. BLETZ THERMOSTAT Filed Jan. 3. 1956 WIITIIII' PRIOR ART/I Fig;4

INVENTOR. HOWARD W. BLETZ United States Pater1t'O THERMOSTAT Howard W. Bletz, Lexington, Ohio, assignor to Stevens Manufacturing Company, Inc., a corporatien cf Ohio Application January 3, 1956, Serial N0. 557,120

13 Claims. (C1. 200-138) The invention relates in general to thermostatg and more particularly t the use of an insulator bushing which is recessed inboard of the flat bearing surfam near the outer periphery of the bushing so a to obtain an aceurately control=led free length 01: birnetallic element used in the thennostat.

The prior art form of thermostats in many instances incorporated a stack of elements which Were mutually separated and insulated by insulator spacers. Where these thermostatg are s-ubjected to high temperatures in the electrical device which they control, the insulator must necessarily be able to withstand such temperatures. Mica and porcelain have been two commonly used insulators. The thermostat often comprises one or more flexible strips carrying eontacts and a bimetallic strip or element to relatively move the contacts. The strips are assembled in a stack, with apertures in each strip aligned and with the insulator spacers separating and insulating these strips. A hollow rivet is often used to fasten the stack together and to the base of -the thermostat.

When porcelain washers o1 spaoers have been used in the past in thermostats, it has been found that the porcelain spacers are not perfeotly flat. The porcelain starts o=ut as a damp powder which :is pressed into a desired shape and then fired to make it hard and in finished form. This firing quite frequently warps the porcelain insulator, and this is the primary cause of opposing surfaces not being planen nor parallel. 'Ihe edges of the porcelain insulator may be curved upwvardly or downwardly from the desired flat plane, and this curvature lying adjacent either a contact strip or the birnetallic strip can change the active free length of the bimetal or of the contact strips. This change of free length changes the amount of resiliency; and when it occurs in the bimetallic strip, it also changes the movement per degree of temperature change. This aifects the temperature differential and aflects the temperature range from low to high osition in an adjustable therrnostat.

Accordingly, an object of the inven-tion is to provide a thermostat wherein the opposite faceof insulator spacers are more nearly planar.

Another object of the invention is to provide an insulator spacer for a thermostat wherein the temperature range between W and high adjustable positions is more nearly constant for successively manufactured thermm stats.

Another object of the invention is to provi de an insulator spacer for a thermostat which has a recess inboard 0f an outer bearing surface to definitely establish the outermost surface cf the insulator spacer as the bearing surface for contact strips and bimetallic strips in the thermostat.

' Anotlrer object of the invention is to provide a thermostat construction utilizing insulating spacers wherein the temperature diflerential between on and oft couditions is more 1iearly uniform between suecessively manufactured thermostats.

' Another objeot of the invention is to provide a thermostat construction wherein the active length of flexible bimetallic element er contact arms is more accurately controlled.

Another object of the invention :is to produce a thermostat utilizing porcelain busllings or other frangible insulator bushings or spacers which are clamped in a stack yet wherein the amount of breaking of such flangible bushings rduring assernbly is materially reduced.

Another object of the invention is to provide a particular shape of an insulator bushing made of a fired porcelain which is cast from a damp powder or the like, which shape assures that, as the damp powder pressing the t0ol 01 die Wears, the porcelain bushings produced will still remain usable.

Other object and a fuller understanding of this invention may be had by referring to the following description and claims, taken in conjunction With the accompanying drawing, in which:

Figure 1 -is a side elevational view partly in section 0f a thermostat embodying the invention;

Figure 2 is a top view of the thermostat of Figure l;

Figure 3 is an enlarged plan view of the insulator bushing used in the thermostat;

Figure 4 is a side view of the bushing;

Figure 5 is a longitudinal sectional view of the bushing of Figure 3; and

Figure 6 is an enlarged sectional view of a prior a.rt form of insulator bushing.

The present invention relates to an improved thermostat which incorporates an improved type of insulator bushing 11 as shown in Figures 3, 4, and 5. This insulator bushing may be used in any of a number of thermostats, and Figures 1 and 2 show for purposes of illustration a typical thermostat 12 With which this insulator bushing may be used. The simple forrn of thermostat 12 shown in Figures 1 and 2 includes a rigid base 13, a stack 14 rigidly fastened to the base 13, an adjusting screw 15, a bimetallic strip 16, and cooperable contacts 17 and 18. The bimetallic strip 16 is typical of any of several constructions in which changes of temperature effect a movement which relatively moves contacts 17 and 18. In this case the two contacts 17 and 18 are shown as carried on contact arms 19 and 20, respectively, With a first end of each containing a circular aperture 21. Terminals 24 and 25 are respectively in contact with the contact arms 19 and 20, and each also has a circular aperture 26 aligned in the stack 14. Two of the insulator bushings 11 are used to mutually separate and insulate the contact arms 19 and 20 and bimetallic strip 16. This bimetallic strip 16 also has an aperture 27 aligned in the stack 14. Another insulator spacer 30 is provided to separate and insulate the upper contact arm 19 and the base 13.

A hollow rivet 32 is used as a clarnping member for the thermostat wo clamp the stack 14 to the base 13. This hol- -low rivet 32 has an enlarged head 33 adjacent the bimetallic strip 16 and a shank 34 extending through the aligned apertures, and this shank may be considered as that which aligns all the apertures. A forrned head 35 formed by pressing er peening is provided adjacent the base 13 to establish axial pressure on the Stack 14.

A nut 38 is fixedly attached to the base 13 and carries the adjusting screw 15 which has an insulating stem 39 acting on the contact arm 20 for adjustrnent cf the coutact 18. This illustrates a typical method of adjustrnent of the operating temperature of the thermostat and is representative cf ways in which the relative spacing between the contacts 17 and 18 may be effected.

The particular shape of the insulator bushings 11 is best shown in Figures 3 4, and 5 and includes generally a washer portion 41 and an axial portion 42. This axial portion extends on only one side of the washer portion 41 v and, as shown in Figure 1 it provides radial separation between the contact arms 19 and 20 and the shank 34. This axial portion 42 is therefore a centering means to accurately align all apertures, especially the apertures in the contact arms 19 and 21), and to make certain that these contact arms are rnutually insulated as weil as electrically insulated from the shank 34 and the rest of the thermostat 12.

The washer portion 41 has a circular periphery 44 and adjacent this periphery are first and second bearing surfaces 45 and 46. These bearing surfaces are annular er washer-shaped and lie in substantially parallel planes. Just inboard of the first bearing surface 45 is a first recess 47 which is disposed between such first bearing surface and the axial portion 42. A second recess 48 is generally axially opposite the first recess 47 but extends completely across the axial portion 42. The depth of these recesses is not great and is preferably in the Order f one-fourth the radial Width of the first recess 47.

The first recess 47 is formed by first and second recessed shoulders 49 and 50 With the first of these being the most important. These shoulders are f0rrned by corners which are relatively sharp but, of course, all such corners are in actual practice roundecl to some degree. The fact that this first recessed shoulder 49 is a relatively sharp corner makes certain that the unter cylindrical surface 51 of the axial portion 42 extends below the plane of the first bearing surface 45 before the fillet o1 rounded corner begins. This is important because the aperture 21 of the contact arm 19 er 20 lies closely adjacent this outer cylindrical surface 51, and it is highly desirable that such contact arm or other contiguous operating element of the therrnostat 12 lie against the bearing surface 45 rather than 011 any such rounded corner.

The insulator bushings 11 are preferably made from a fired porcelain which initially exists as a damp powder 01' the like and is pressed or molded into shape by a pressing o1 forrning to0l or die. Such pressing toel must necessarily have a sl1a1p outer corner t0 form the first recessed shoulder 49. As this pressing tool wears, this outer corner will become less sharp and thus create a continually greater and greater raclius fillet at the first recessed shoulder 49 in the final porcelain bushing 11. Thus, by initially providing the recesses 47 and 48, the porcelain bushings 11 are usable even after the porcelain pressing tool wears considerably.

After the darnp powder is pressed into shape, it is fired and during this firing which makes the percelain into the hard finished product, warping and twisting inevitably occurs. The Figure 6 shows a prior art form of porcelain bushing 54 which did not contain any recesses on the Washer Portion 55. The broken lines 56 show that the edges of the washer ortion 55 may warp downward slightly during firing 01 the brol en lines 57 indicate that this porcelain bushing may warp upwardly to a greater 0r less extent during firing. lt Will be noted from Figure 1, the distance fr0rn the center line 59 to the edge of the porcelain bushing is not great compared to the free length of the birnetallic strip 16 or contact arrns 19 and 20. Thus, if the washer portion 55 should warp upwardly as shown by the broken line 57, then it would not be nearly as definite a fulcrurn er abutrnent about which the flexible element Will bend. T bis means that the active length 0f bimetal is variable between successively manufactured ther mostats, and thus the temperature differential between on and oft" conditions of the contacts 17 and 18 will vary widely and also the temperature range between high and 10W adjustment position of the adjustment screw 15 will also have wide variations.

The insulator bushing 11 cf the prcsent invention shown in Figures 3, 4, and matcrially reduces such variations in active length of therrnostat elements, it materially reduces the temperature differential cf the thermostat,

and it materially reduces the temperature range between 1 high and low positions is quite pronounced in the snapacting type of thermostats, such as is shown in Patent N0. 2,692317 issued October 19, 1954, to Edward Bletz. When the improved forrn of insulator bushing 11 is used in such snap-acting type of thermostat, the erformance of such thermostat is considerably improved to make more uniform successively manufactured therrnostats.

During assembly of the therm0stat 12, 01" any such thermostat utilizing a stack of a plurality cf elements, the hollow rivet 32 is placed through the aligned apertures and then spun, peened, 0r pressed over to form the formed head 35. During such operation an axial force is applied to the stack 14 so as to tightly assemble all elements in the stack. Fast experience has shown that for a particular force applied to the stack breakage cf one or more cf the insulator bushings er spacers 11 and 30 was approximately 5 percent, with the old prior art forrn of insulators. Utilizing the same thermostat construction and the same axial force during rivet head forming operations, the breakage of insulators has been reduced to about 1 to 2 percent; and thercfore, this is about a 200 percent increase in manufacturing efficiency on this one operation alone to thus reduce scrap losses. The reason for the redueed breakage of insulators is believed to be that the bearing surfaces 45 and 46, being shorter in radial extent, have less total Warpage away from the desired flat planar condition; and therefore, localized positions of high unit stress 0n the porcelain bushings are avoided. Because there is less total warpage, there is a m0re constant active length cf. birnetallie strip 01' contact arms to give more uniform therrnostat operating conditions including temperature diflerential and temperature range. Also, the warpage, whatever there is of it during the firing cf the porcelain, is confined to areas of the bushings which a1e closer to the outer periphery than in the prior art form. For example, under the extreme and exaggerated condition 015 upward warping, as shown in Figure 6, the fulcnum for the bimetallic element would be at point 60 rather than at point 61; and this would greatly afiect the active length of bimetallic strip. Hewever, in the approved form of thermostat, if the porcelain bushing should warp upwardly to a very great extent, the fulcrum point would be at point 62 rather than at point 63 and this would not change the operating conditions cf the thermostat nearly as rnuch as if the fulcrum were at point 64 which corresponds to the point 60 on the prior art form of bushing.

The recesses 47 and 48 being inboard cf the bearing surfaces 45 and 46 establish that the axial pressure on the stack 14 will be borne at the bearing surfaces 45 and 46 which is near the outer periphery of the insulator bushings 01 spacers to thus establish that the active free length of bimetallic strip will always begin adjacent the outer periphery of such insulator bushings.

Although this invention has been described in its preferred forrn with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of exarnple and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope cf the invention as hereinafter claimed.

What is claimed is:

1. A therrnostat cornprising, a base, a bimetallic element, an insulator spacer mutually insulating said base and bimetallic element, clamping rneans acting on said base, element and spacer to clamp same together in a stack, a first circular bearing surface adjacent the outer periphery of said spacer, a first recess on one side of said spacer inboard cf said bearing surface, a second circular bearing surface generally axially opposite said first bearing surface to also lie adjacent to the outer periphery of said spacer, a second recess on the opposite side of said bushing of substantially equal diameter as the first recess, and said first and second bearing surfaces lying in substantially parallel planes, whereby said clamping means exerts an axial pressure 011 said stack which is borne by said first and second bearing surfaces rather than at the recesses of said spacer to thereby establish a definite free length of bimetallic element.

2. A thermostat comprising, a base having an aperture, a bimetallic element having an aperture, an insulator bushing mutually insulating said base and bimetallic element, a clamping member having a shank passing through said apertures and bushing to place them in substantial alignment and to create a stack and clamping said bimetallie element to said base, a washer portion on said bushing, an elongated axial portion on said bushing extending on only one side of said washer portion, a first annular bearing surface adjacent the outer pen'phery of said bushing, a first recess on one side of said bushing between said axial portion and said first bearing surface, a second annular bearing surface generally axially opposite said first bearing surface to also lie adjacent to the outer periphery of said bushing, and a second recess on the opposite side of said bushing of substantially equal diameter as the first re cess and extending across said axial portion, Whereby said clamping member exerts an axial pressure on said stack which is borne by said first and second bearing surfaces rather than at the recesses of said bushing to thereby establish a definite free length of bimetallic element.

3. An insulator spacer for a thermostat comprising, a first circular bearing surface adjacent the outer periphery of said spacer, a first recess on one side of said spacer, inboard of said bearing surface, a second circular bearing surface generally axially opposite said first bearing surface to also lie adjacent to the unter periphery of said spacer, a second recess on the opposite side of said bushing of substantially equal diameter as the first recess, and said first and second bearing surfaces lying in substantially parallel planes.

4. An insulator bushing for spacing a flexible bimetallie element in a thermostat, comprising, a washer portion on said bushing, a first annular bearing surface adjacent the outer periphery of said washer portion, a first recess on one side f said bushing inboard of said first bearing surface, a second annular bearing surface generally axially opposite said first bearing surface to also lie adjacent t0 the outer periphery of said washer portion, and a second recess on the opposite side of said bushing cf substantially-equal diameter as the first recess.

5. An insulattor bushing for spacing and insulating flexible members in a thermo-stat, comprising, a washer portion on said bushing, an elongated axial portion on said bushing extending on only one side of said Washer portion, a first substantially annular bearing surface adjacent the outer periphery of said bushing, a first recess on one side of said bushing between said axial portion and said first bearing surface, the depth of said first recess being approximately one-fourth the width thereof between said first bearing surface and said axial portion, a second substantially annular bearing surface generally axially opposite said first bearing surface to also lie adjacent to the outer periphery of said bushing, and a second recess on the opposite side of said bushing extending across said axial portion.

6. An insulator bushing for spacing and insulating flexible members in a thennostat, comprising, a washer portion on said bushing, an elongated axial portion on said bushing extending on only one side of said washer portion, a first substantially circular bearing surface adjacent the outer periphery 0f said bushing, a first substantially coaxial recess on one side of said bushing between said axial portion and said first bearing surface, the depth of said first recess being approximately one-fourth the width thereof between said first bearing surface and said axial portion, a second annular bearing surface generally axially opposite said first bearing surface to also lie adjacent to the outer periphery of said bushing, a second substantlally coaxial recess on the opposite side of said bushing of substantially equal diameter and depth as the first recess and extending across said axial portion, and said first and second bearing surfaces lying in substantially parallel planes.

7. A thermostat comprising, a base having an aperture, a contact arm and an elongated bimetallic strip each having an aperture at one end thereof, an electrical terminal touching said contact arm and having an aperture sub stantially coinciding therewith, at least one insulator bush ing mutually insulating said contact arm and bimetallic strip, a hollow rivet having a head and having a hollow shank passing through said apertures and bushing to place them in substantial alignment and to create a stack, a formed head on said hollow rivet acting as a clamping member to clamp said bushing, arm, terminal and strip together in said stack, a washer portion on said bushing, an elongated axial portion 011 said bushing extending on only the adjacent contact arm side cf said washer portion, a first annular bearing surface adjacent the outer periphery of said bushing, a first recess on one side of said bushing between said axial portion and said first bearing surface, the depth of said first recess being approximately one-fourth the width thereof between said first bearing surface and said axial portion, a second annular bearing surface generally axially opposite said first bearing surface to also lie adjacent to the outer periphery of said bushing, and a second recess on the opposite side of said bushing of substantially equal diameter as the first recess and extending across said axial portion, whereby said hollow Iivet by the two heads thereof exerts an axial pressure on said stack which is borne by said first and second bearing surfaces rather than at the recesses of said bushing to thereby establish a definite free length of bimetallic strip and contact arm.

8. A thermostat comprising, a base, a plurality of coutact arms and a bimetallic strip each fastened together at one end thereof in a stack, apertures in said arms and strip in alignrnent in said stack, a hollow rivet having a head and passing through said aligned apertures, fired porcelain bushings in said stack mutually separating said contact arms and bimetallic strip from said hollow rivet, a peened head on said hollow rivet adjacent said base acting as a clamping member to clamp said bushings, arms, and strip together in said stack, electrical terminals in said stack adjacent each of said contac-t arms, a washer portion on each of said bushings, an elongated axial portion on each of said bushings adjacent said conta-ct arms and extending on one side cf said washer portion, a first annular bearing surface contiguous With the outer extremity of said bushing, a first substantially coaxial recess on one side 0f said bushing between said axial portion and said first annular bearing surface, the depth of said first recess being approximately one-fourth the width thereof between said first bearing surfiace and said axial portion, a second annular bearing surface generally axially opposite said first bearing surface to also lie contiguous to the outer periphery of said bushing, and a second substantially coaxial recess recessed from said second bear-ing surface on the opposite side of said bushing of substantially equal diameter and depth as the first recess and extending across said axial portion, said first and second bearing surfaces being substantially parallel and perpendicular to the axis of said rivet, whereby said hollow rivet by the peened head thereof exerts an axial pressure on said stack which is borne by said first and second bearing surfaces rather than at the recesses of said bushings to thereby establish a definite free length of birnetallic strip and contact arms.

9. A thermostat comprising, a base having a circular aperture, a plurality of elongated flexible contact arms and an elongated birnetallic strip each having a circular aperture at one end thereof, an electrieal terminal touching each of said contact arms and each having an aperture substantially coinciding with that of the cont=iguous contact arm, fired porcelain bushings mutually insulating and separating said contact arms and bimetallic strip, a hollow rivet having a head adjacent said bimetallic strip and having a hollow shank passing through said apertures and bushings to plane thern in substantial alignment and to create a Stack, a formed head on said hollow rivet adjacent said base on the opposite side from said Stack acting as a clampin'g member to clamp said bushings, arms, terminals and strip together in said stack, a washer portion on each of said bushings, an elongated axial portion on each of said bushings extending on only the adjacent comtact arm side of said Washer portion, a first annular bearing surface contiguous to the outer periphery of said bushing, a first substantially coaxial recess on one side of said bushing between said axial portion and said first bearing surface, the depth of said fiist recess being approximately one-fourth the width thereof between said first bearing surfaee and said axial portion, a second annular bearing surface generally axially opposite said first bearing surface to also lie contiguous to the outer periphery o f said -bushing, a second substantially coaxial recess on the opposite side of said bushing cf substantially equal diameter and depth as the first recess and extending across said axial portion, and said first and second bearing surfaces lying in substantially parallel planes, whereby said hollow rivet by the two heads thereof exerts an axial pressure on said stack which is borne by said first and second bearing surfaces rather than at the recesses cf said bushings to thereby establish a definite free length 0f bimetallic strip and contact arms.

1.0. An insulator spacer for a thermostat comprising, a first bearing surface adjacent at least part of the outer periphery of said spacer, a TCCSS on one side of said spacer inboard of said bean'ng surface, a second bearing surface generally axially opposite said first bearing surface to also lie adiacent part cf the outer periphery of said spacer, and said first and second bearing surfaces lying in substantially parallel lanes.

l1. An insulator spacer for a thermostat comprising, a first bearing sunface adjacent at least art of the outer periphery cf said spacer, a first recess on one side cf said spacer inboard of said bearing surface, a second bearing surface generally axially opposite said first bearing surface to also lie adjacent to part of the outer periphery cf said spacer, a second recess on the opposite side cf said bushing of substantially the same size as the first recess, and said first and second bearing surfaces lying first bearing surface to also lie adjacent to part of the outer periphery of said spacer, and a second recess on the opposite side of said bushing cf substantially the Same size as the first recess, whereby said clamping member exerts an axial pressure on said stack which is vorne by said first and second bearing surfaces rather than at the recesses of said spacer to thereby establish a definite free length of bimetallic element.

13. A thermostat comprising, a base having an aperture, a bimetallic element having an aperture, an insulator bushing rnutually insulating said base and bimetallic element, a clarnping rnember having a shank passing through said apertures and bushing to place them in substantial alignment and to create a stack and damping said bimetallic element to said base, a washer portion on said bushing, an elongated axial portion on said bushing extending on only one side of said washer portion, a first bearing surface adjacent at least part of the outer periphery of said bushing, a first recess on one side of said bushing between said axial portion and said first bearing surface, a second annular bearing surface generally axially opposite said first bearing surface to also lie adjacent to a part of the outer periphery of said bushing, and a second recess on the opposite side of said bushing of substantially the same size as the first recess, whereby said clamping member exerts an axial pressure on said stack which is borne by said first and second bearing surfaces rather than at the recesses of said bushing to thereby establish a definite free lengt'n 0f bimetallic element.

References Cited in the file of this patent UNITED STATES PATENTS Dafforn Apr. 20, 1943 Lee Sept. 21, 1954

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