US2720568A - Snap-acting bimetallic thermostat - Google Patents

Description

Oct. 11, 1955 TE M P.

E. BLETZ SNAP-ACTING BIMETALLIC THERMOSTAT Filed Jan. 27, 1953 ICO IOO/

INVENTOR.

TIME

BY EDWARD BLETZ nited States Patent SNAP-ACTlN G BIMETALLIC THERMOSTAT Edward Bletz, Lexington, Ohio, assignor to Stevens Manufacturing Company, Inc., a corporation of Ohio Application January 27, 1953, Serial No. 333,404

Claims. (Cl. 200-138) The invention relates in general to thermostats and more particularly to snap-acting thermostats. This invention is an improvement over my co-pending application Serial No. 207,382, filed January 23, 1951, now Patent No. 2,692,317, entitled Snap-Acting Thermostat. Snap-acting thermostats inherently have a greater differential than the so-called creep type of thermostat. The differential is the temperature range between open and closed positions of the contacts or operating portions of the thermostat. Creep type thermostats are those wherein the bimetallic element or temperature responsive element is a strip or other configuration which gradually deflects upon temperature changes. Snap-acting thermostats are those wherein there is provided some form of snap-acting or over-center device which has alternate positions of static equilibrium on either side of a neutral axis. Creep type thermostats may have a differential of say two or three degrees, whereas the usual snap-acting thermostats may have a differential of ten to twenty degrees. Snap-acting thermostats are primarily used wherein the radio interference is desired to be eliminated since the snap-action of the electrical contacts quickly makes and breaks the electrical circuit; thus, there is no arc to cause radio interference. Further, since there is no arc of any prolonged duration, there is appreciably less pitting and burning of electrical contacts to thus give a longer useful life of these contacts.

The present invention relates to a snap-acting thermostat which has a considerably smaller differential than the conventional snap-acting thermostat, and this is achieved by combining both creep and snap-acting temperature responsive elements into a single thermostat to thus gain the advantages of both types.

An object of the invention is to provide a combined snap-acting and creep type thermostat which has the small operating differential of the creep type and has the rapid make and break of the contacts of the snap-acting type.

Another object of the invention is to provide a snapacting thermostat with a snap-acting link which is temperature responsive by itself.

Another object of the invention is to provide a thermostat wherein a creep bimetal moves two contacts in the same direction and wherein a snap-acting bimetal moves the contacts in opposite directions.

Another object of the invention is to provide a snapacting link for a snap-acting thermostat wherein the link has tension and compression members to provide an over-center structure and wherein at least a part of this link is bimetallic or temperature responsive. An additional object is to make the tension members of the snap-acting link temperature responsive.

Another object of the invention is to provide a thermostat having two contacts or operating portions wherein both contacts are moved by one temperature responsive means or bimetallic means and only one of these contacts is moved by a second temperature responsive means or bimetallic means. Additionally, it is an object of the invention to make the second bimetallic means a snap- 2,720,568 Patented Oct. 11, 1955 acting link to provide quick make and break of the contacts.

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

Figure 1 is a side elevational view of an electrical thermostat embodying the invention;

Figure 2 is a plan view of over-center spring member removed from the thermostat;

Figure 3 is a side view of the spring member of Figure 2;

Figure 4 is a plan view of a modified form of overcenter spring member;

Figure 5 is a side view of the spring member of Figure 4; and

Figure 6 is a graph of temperature versus time, comparing conventional snap-acting thermostats with that of the present invention.

The Figure 1 generally shows the complete snap-acting thermostat wherein a base is indicated at 15 and a stack is indicated at 16. The base 15 carried a nut 17 which is fastened thereto by any suitable means such as welding or swaging. The nut 17 has a stop portion 18. A shaft 19 has a screw portion 20 threadably in the nut 17 and is adapted to receive a manually operable handle, not shown. The shaft 19 has a stop lug 22 which will engage either side of the stop portion 18 to provide limits of rotation of the shaft 19 relative to the nut 17. The lower end of the screw 20 extends through the base 15 and carries an insulating tip 23.

The stack 16 includes an over-center spring member 24, a flexible contact strip 25, and a flexible bimetallic strip 26. Each of these strips 24, 25, and 26 are elongated pieces of metal which lie generally parallel and have the left ends thereof firmly fastened into the stack 16. An electrical terminal 27 is in electrical contact with the spring member 24, and an electrical terminal 28 is in electrical contact with the contact strip 25. A hollow rivet 29 firmly fastens the entire stack 16 to the base 15. The stack 16 includes three insulating washers 30 which mutually insulate the base 15, the spring member 24, the contact strip 25, and the bimetallic strip 26. The over-center spring member 24 is better shown in Figures 2 and 3 wherein this member is shown as being removed from the stack 16. This spring member 24 includes first, second, and third spring strips 31, 32, and 33. The first and third spring strips 31 and 33 are formed of bimetal and are spot welded, as at 34, to the over-center spring member 24. The outer or first and third spring strips 31 and 33 are V-crimped, as at 35, in order to slightly shorten the length thereof. This places the strips 31 and 33 in tension and the strip 32 in compression; hence, the strip 32 will bow one side of a neutral axis as is shown in Figures 1 and 3. When the spring member 24 is assembled in the stack 16, the center spring strip 32 is adapted to be contacted by the insulating tip 23 to slightly flatten the curvature of this strip 32.

An insulating spacer 51 is carried by the flexible contact strip 25 as by the tongue 52 passing through a hole 53. The insulating spacer 51 has sufficient height to bear against the under side of the second spring strip 32 and bow the same upwardly even though the insulating tip 23 may be raised to its upper limit as shown in Figure l.

The free end of the spring member 24 carries on the lower side thereof an electrical contact 40, and the free end of the contact strip 25 carries on the upper side thereof a second electrical contact 41. These contacts 40 and 41 are shown in Figure 1 as being in physical contact. The free end of the contact strip 25 further carries a U-shaped portion 4-2 which surrounds the end of the spring member 24. The U-shaped portion .2 has a threaded aperture 43 which carries an adjusting screw 44. This screw 44 has an insulating tip 45 which is disposed near but spaced from the upper side of the free end of the spring member 24. The distance between the insulating tip 45 and the contact 41, less the thickness of the contact 40 and the strip 24, determines the spacing of the contacts in the open circuit position. Changes in this spacing also change the operating differential of the thermostat. The bimetallic strip 26 carries an insulating button 46 shown in contact with the lower side of the free end of the contact strip 25.

Operation If one considers that the over-center spring member 24 is not bimetallic, then the operation of this thermostat is essentially that shown and described in my co-pending application. As the temperature changes in a given sense, the bimetallic strip 26 will move upwardly; and this will move the free end of the spring member 24 upwardly until it passes through the neutral position whereupon this spring member 24 will snap over-center to the alternate position of static equilibrium. This will mean that the upper side of the spring member 24 is in contact with the insulating tip 45, and the contacts 40 and 41 will no longer be in contact. It is assumed that the terminals 27 and 28 are connected in an electrical circuit which, when the contacts 40 and 41 are closed, controls the circuit to make the temperature change in the aforementioned given sense. Further, when the contacts are opened, the electrical circuit is conditioned so that the temperature will change in the opposite sense. This means that the bimetal strip 26 will start to move downwardly; hence, the insulating tip 45 will move the spring member 24 downwardly until it again snaps over-center to close the contacts 40 and 41.

The bimetallic strips 31 and 33 are temperature responsive in the same direction as the bimetallic strip 26 for temperature changes of a given sense. Thus, as the temperature rises and the strip 26 moves upwardly, for example, the strips 31 and 33 will also exert a force to move the contact 40 upwardly. In fact, if the spring member 24 separated from the thermostat as shown in Figures 2 and 3, were subjected to temperature changes, at some temperature, the spring member 24 would snap over-center to the opposite position and would then snap back again upon the temperature moving back toward its original condition. It is thus seen that the action of the bimetallic strips 31 and 33 is to aid the action of the bimetallic strip 26.

The graphs of Figure 6 are graphs showing temperature versus time. .A curve 55 is shown for a conventional snapacting thermostat, and a curve 56 is shown for the snapa'cting thermostat of the present invention. The two thermostats under test were as identical as possible with the only difference being that the conventional thermostat was constructed as shown in Figure 6 of my co-pending application and the thermostat providing curve 56 was constructed in accordance with Figures 1, 2, and 3 of this application. The difference between the two thermostats was then that the spring members 31 and 33 were bimetallic rather than being of ordinary spring material. The bimetals used in each thermostat was a number 6650 birnetal and the adjustments were the same; namely, a .005 inch spacing between the contacts 40 and 41 in the open condition. The area 57 on the curve 55 shows the operating diiferential when the standard thermostat was set for an operating temperature of about one hundred fifty-five degrees. The differential was twelve to fifteen degrees in this case. The area 58 on the curve 56 shows the thermostat of the present invention set for approximately one hundred fifty-two degrees, and it will be seen that the temperature differential was about three to four degrees. The area 59 on the curve 55 shows the conventional thermostat adjusted for a higher operating temperature of approximately two hundred twenty degrees, and it will be seen that the operating differential is approximately thirteen degrees. The area 60 on the curve 56 is a curve of the temperature produced by the thermostat of this invention when adjusted for approximately two hundred two degrees and shows that the operating differential is approximately three degrees. These graphs were obtained from a recording thermometer under conditions controlled to be as nearly identical as possible. These curves and 56 show that the conventional snapacting thermostat has an operating temperature differential approximately four times as large as that of the thermostat of the present invention.

The Figures 4 and 5 show a modified form of overcenter spring member 62. This spring member 62 includes first, second, and third spring strips 63, 64, and 65 which are all formed from a single piece of metal. Elongated apertures 66 in this spring member 62 cause the separation thereof into these three spring strips. The entire spring member 62 is formed from birnetal; and hence, the action of this spring member 62 under temperature changes is approximately the same as that of the over-center spring member 24.

The bimetallic strip 26 is a creep action bimetal, and the over-center spring members 24 or 62 are combined snap-acting means and temperatures responsive means. The bimetallic strip 26 moves upwardly; and hence, moves both contacts 41 and 40 upwardly. The snap-acting spring member 24 or 62 moves only the contact 4% upwardly upon temperature changes of the same sense.

Although this invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example 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 of the invention as hereinafter claimed.

What is claimed is:

1. A thermostat comprising, a base, first and second operating portions mutually co-operable, creep action temperature responsive means on said base to move both said first and second operating portions in a first direction upon a temperature change in a given sense, and combined snap-acting means and second temperature responsive means on said base to relatively move said first and second operating portions in opposite directions upon temperature changes in said given sense.

2. A thermostat comprising, a base, first and second contacts mutually co-operable, creep action temperature responsive means on said base to relatively move said first and second contacts into tighter mutual engagement upon a temperature change in a given sense, and combined snapacting means and second temperature responsive means on said baseto relatively separate said contacts upon a temperature change in said given sense.

3. A thermostat comprising, a base, first and second contacts mutually engageable, creep action temperature responsive means on said base to move both said first and second contacts in a first direction upon a temperature change in a given sense and to move them into tighter mutual engagement, and combined snap-acting means and second temperature responsive means on said base to quickly move only said second contact in said first direction a greater distance than said first contact is moved by said first temperature responsive means to separate said contacts upon a temperature change in said given sense.

4. A thermostat comprising, a base, first and second operating portions mutually co-operable, creep action temperature responsive means on said base to move both said first and second operating portions in a given direction upon a temperature change in a given sense, and snap action temperature responsive means on said base to relatively separate said first and second operating portions upon a temperature change in said given sense, said temperature responsive means acting in combination to provide a smaller operating temperature difierential than said snap action means alone.

5. A thermostat comprising, a base, first and second operating portions mutually co-operable, creep action temperature responsive means on said base to move said first operating portions through said second operating portion upon a temperature change in a given sense, and snap-action temperature responsive means on said base to relatively separate said first and second operating portions upon a temperature change in said given sense.

6. A snap-acting thermostat comprising a base, a stack of strips on said base, said stack of strips including a bimetallic strip, a contact strip, and a snap-acting strip, said snap-acting strip having a compression member and a tension member to permit said snap-acting strip to snap over-center to a position of static equilibrium on either side of a neutral axis, at least said tension member of said snap-acting strip being bimetallic, a first contact carried on said contact strip and movable by said bimetallic strip, a second contact movable by said snap acting strip for co-operation with said first contact, current passable through said contacts, said contact strip and said snap acting strip and excluding said bimetallic strip, screw means on said base to adjustably position said snapacting strip, a stop movable with said first contact and bearable against the rear of said second contact, and said bimetallic strip and tension member movable in the same direction upon temperature changes in a given sense.

7. A snap-acting thermostat comprising a base, a stack on said base, a bimetallic strip, a contact strip, and a snap-acting strip carried on said stack, said snap-acting strip having a compression member and a tension member to permit said snap-acting strip to snap over-center to a position of static equilibrium on either side of a neutral axis, said tension member being temperature responsive, a first contact carried by said contact strip, a second contact carried by said snap-acting strip for cooperation with said first contact, screw means on said base to adjustably position said snap-acting strip, said tension member and bimetallic strip movable in the same direction upon temperature changes in a given sense, and said contact strip movable by said first bimetallic strip for initial movement of both contacts with temperature changes in a given sense and said snap acting link providing final movement of said second contact to separate said contacts.

8. A snap-acting thermostat comprising a base, a stack on said base, a bimetallic strip, a contact strip, and a snap-acting strip carried in that order on said stack, said snap-acting strip having a compression member flanked by two tension members to permit said snap-acting strip to snap over-center to a position of static equilibrium on either side of a neutral axis, said two tension members being bimetallic, a first contact carried by said contact strip, a second contact carried by said snap-acting strip for cooperation with said first contact, an adjustable screw threaded in said base and rotatable to move said compression member, a stop carried by said contact strip and moving therewith and bearable against the snap-acting strip on the side thereof opposite said second contact, said bimetallic strips movable in the same direction upon temperature changes in a given sense, said contact strip movable by said first bimetallic strip, and abutment means bearing against said compression member on the side thereof opposite said adjustable screw.

9. A snap-acting thermostat comprising a base, a stack on said base, a bimetallic strip, a contact strip, and a snap-acting strip carried in that order on said stack, said snap-acting strip having a compression member flanked by two tension members to permit said snap-acting strip to snap over-center to a position of static equilibrium on either side of a neutral axis, said two tension mem bers being bimetallic and said compression member being nonresponsive to temperature changes, a first contact carried by said contact strip, a second contact carried by said snap-acting strip for co-operation with said first contact, an adjustable screw threaded in said base and rotatable to move said compression member, a stop carried by said contact strip and moving therewith and bearable against the snap-acting strip on the side thereof opposite said second contact, said bimetallic strips movable in the same direction upon temperature changes in a given sense, said contact strip movable by said first bimetallic strip, and abutment means bearing against said compression member on the side thereof opposite said adjustable screw.

10. A snap-acting thermostat comprising a base, a stack on said base, a bimetallic strip, a contact strip, and a snap-acting strip carried in that order on said stack, said snap-acting strip having a compression member flanked by two tension members to permit said snap-acting strip to snap over-center to a position of static equilibrium on either side of a neutral axis, said entire snap-acting strip being bimetallic, a first contact carried by said contact strip, a second contact carried by said snap-acting strip for co-operation with said first contact, an adjustable screw threaded in said base and rotatable to move said compression member, a stop carried by said contact strip and moving therewith and bearable against the snap-acting strip on the side thereof opposite said second contact, said bimetallic strips movable in the same direction upon temperature changes in a given sense, said contact strip movable by said first bimetallic strip, and abutment means bearing against said compression member on the side thereof opposite said adjustable screw.

References Cited in the file of this patent UNITED STATES PATENTS 2,139,921 Weinhardt Dec. 13, 1938 2,236,699 Riche Apr. 1, 1941 2,246,309 Lee June 17, 1941 2,440,025 Singleton Apr. 20, 1948

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