US2824192A - Thermally actuated switch - Google Patents

Description

2 sheets-shew 1 A. B. MARMO Feb. 18, 1958 THERMALLY CTUATED SWITCH Filed Oct. 5. 19'56 n /V/.V//VV/V/ o l M O O A A m 1 mM. m Mm Fw, f MH Ml 8 m m////////%////% im w MQ. n n@ o ...wf m W. 56 www.: m A m m m w OM/U E Lmwm 5 l m W Q H. A l- I mw. l M u Wm Q s m@ A f u.. Y N 7////////// G vm, H H :3 m Il F .1

ATTORNEY Feb. 18, 1958 .A. B. MARMO THERMALLY ACTUATED SWITCH 2 Sheets-Sheet 2 Filed Oct. 5, 1956 SEMBLY A,

INVENTOR NTHoNY BMARMO ATTORNEY F IGA nite 'rHnnMALLY ACTUATED SWITCH Application October 5, 1956, Serial No. 614,170

Claims. (Cl. 2ll-122) This invention relates to a thermally actuated switch structure and particularly to an improved thermal cycling, wattage control switch utilizing one bimetal for cycling the switch and a second bimetal providing ambient temperature compensation.

Among the objects of this invention are to improve the construction and performance and reduce contact wear in a thermally actuated switch and to simplify the adjusting means for a switch of this type.

A further object of this invention is to improve the construction and performance of a thermal cycling switch which includes only a single thermomotive member for cycling the switch contacts and a single thermomotive member providing ambient temperature compensation.

A still further object of this invention is to improve the construction of the aforementioned type of switch so that a majority of the switch components may be completely assembled as a unit before being mounted in a switch enclosure.

ln accordance with this invention, there is assembled on a switch stack a cyclically operating switch comprising a pair of relatively movable contacts and a bimetal actuator that opens the switch in response to heat conducted to it from a heat storage bar. The bar has an electric heater connected in series with the switch contacts. The bimetal, upon cooling, effects reclosure of the contacts. This switch, when connected to an electric power source in series with a load, may be adjusted to continuously cycle to control the power to the load. The bimetal is connected in good heat transfer relationship with the heat storage bar but is so arranged with respect thereto that temperature changes in the bimetal lag the temperature changes in the storage bar when the latter is both heated and cooled. The time lag in the conduction of heat from the heat storage bar to the bimetal causes the latter to continue deflecting in contact opening direction after the cycling switch is opened and in contact closing direction after this switch is closed to provide a positive make and break of the switch contacts, thus improving the switch performance and prolonging contact life.

The switch of the invention also includes novel adjusting means comprising a cam that is operated by an adjusting shaft extending through the stack of switch components.

The foregoing and other objects are effected by the invention as will be apparent from the following description taken in connection with the accompanying drawings, forming a part of this application, in which:

Fig. l is a vertical section of a thermal cycling switch taken along line I--I of Fig. 2;

Fig. 2 is a vertical section taken along the line II--II of Fig. l;

Fig. 3 isr a schematic diagram showing the electrical circuit for the switch and the connections for a heater to be controlled thereby; and

Fig. 4 is an exploded view of the operating elements of the switch of Figs. 1 and 2.

rates Patent O 2,824,192 Ptented Feb. 18, 1958 Referring to Fig. l of the drawings, an adjustable wattage control 10 includes a thermal cycling switch 12, a line switch 14 and a pilot light switch 16 mounted in an enclosure comprising an open-top box-shaped casing 18 and a plate 20 that closes the casing. All of the movable contacts in these switches are assembled on resilient strips that are clamped in stacked relationship by a tubular rivet 21. The components in this stack are indicated as assembly A in Fig. 4.

The cycling switch 12 includes an adjustable contact 22 mounted on the free end of a resilient strip 24. A cycling contact 26 is positioned to cooperate with the adjustable contact 22 by means of `a resilient strip 28, also secured in the stack. One end of the strip 28 extends beyond the cycling contact 26 and is actuated by an electrically insulating ceramic pin 30 that is secured to the detlectable end of a bimetallic strip 32. The other end of the bimetal strip 32 is brazed or otherwise connected in good heat conducting relationship to a rigid heat storage bar 34 and is clamped therewith in the switch stack. The bar 34 has a heater 36 clamped thereto and electrically insulated therefrom. This bar extends from the stack in angularly spaced relationship with respect to the detlectable portion of the bimetallic strip to minimize the effect of radiant heat from the bar on this portion of the strip. The heater 36 comprises a thin ribbon-like resistance element 37 formed in a flat loop and clamped to the bar 34 between a pair of insulating washers. This heater may be stamped from a thin at sheet of metal having the desired resistance characteristics. One end of the element 37 is connected to a conducting plate 38 welded to the strip 24 and secured in the stack. The other end of the element 37 is connected to a terminal 40 extending from the stack and through the insulated casing 18 (Fig. 2). The strip 28 supporting the cycling contact 26 is welded at its fixed end to a terminal strip 42 that also is clamped in the stack and extends through the casing 18 (Fig. l).

The bimetal strip 32, the resilient contact supporting strips 24 and 28 and the terminal 40 are all electrically insulated from each other in the stack assembly by suitable insulating sleeves and washers. Also supported within the switch stack in insulated relationship with respect to the above mentioned switch elements is a resilient plate 50 that is welded to a terminal 52. One end of the plate 50 extends at one side of the switch stack and has a recess S3 into which projects one end of an electrically insulating ceramic pin member 54. This pin extends through an opening in the resilient strip 28 and its other end iits into a recess 55 in the adjustable contact supporting strip 24. The strip 24 and the end of the plate 50 engaged by the pin 54 are inherently biased toward each other so that the pin 54 is retained therebetween, but the strip 24 has a spring force that is stronger than that of the plate 50 so that the boss 53a on the opposite face of the latter formedby the recess 53 will be biased against an active surface S8 of a cam plate 60 to be described hereinafter.

The components of the stack assembly, indicated at A in Fig.'4, are secured together and to the cover 2f; by means of the rivet 21 having a head S6 at lone end located above the cover plate 20. The rivet has a tubular portion extending through the plate 2t) and downwardly therefrom through the components of the stack assembly, the lower end of the rivet being peened against a metal washer 57 to clamp these components in fixed relationship. The bimetal 32 is free to deect without interference by the cover plate 20 and is spaced therefrom by an insulating washer 59. The cover is cut away opposite the outer end of the bimetal to permit the latter to deflect a greater distance in the contact closing direction.

The cam plate 60 has a central polygonal opening 61 within which is located a complementary polygonal cam driving member 62 that is keyed to a switch operating shaft 63. i The shaft 63 extends through the tubular portion of the rivet 21 which forms a bearing surface for rotatably supporting the shaft. The upper end of the shaft 63, as seen in the drawings, may be connected to any suitable manual operating means or knob (not shown). The flat face of the cam 60 opposite the active surface 58 is supported by two bosses 66 and 67 on the casing and by a third boss 68 on the low expansion side of an ambient temperature compensating bimetal strip 76 located in a channel 71 in the casing 18.

The cam 60 is rotatable about theraxis of the shaft 63 and lits loosely about the polygonal member 62 so that it may pivot about a line connecting the tops of the two bosses 66 and 67. This pivotal movement occurs when the boss 68 on the ambient temperature compensating bimetal 7) is moved relative the casing 18 in response to either bowing of the bimetal due to a change in ambient temperature or manual adjustment of the bimetal 7). One end of the compensating bimetal 70 rests on the casing 18 and the other end is supported by an adjustable screw 72. By raising or lowering the adjustable screw 72, the boss 68 on the bimetal may be adjusted to tilt the cam 6l) about its pivotal axis on the bosses 66 and 67. Thus, the switch may be calibrated to select the temperature of the bimetal 32 at which the switch 12 is opened and thus provide, for a given shaft position, a predetermined duty cycle or percentage of closed contact time of this cycling switch during its cycling operation.

The cam 6i) may be rotated by the shaft 63 to select the desired duty cycle of the switch 12. The shaft 63 may be adjusted to an off position in which the cam 6i) is positioned with the highest portion 58h of the cam surface 58 in engagement with the boss on the plate 56 to hold switch 12 open. In this Voff position the switches 14 and 16 are held openV by means described hereinafter. When the shaft 63 is moved from the off position the switches 12, 14 and 16 are closed and the percentage of closed contact time of the switch 12 will be determined by the height of the portion of the cam surface 53 engaged by the plate 50. As this height is progressively varied from maximum to minimum by rotation of the cam, the percentage of closed contact time of switch 12 is varied from minimum to maximum.

Located in the bottom wall of the casing and coaxial with the shaft 63 is a circular recess 74 within which lies a spring 75 held in compression between the lower side of the polygonal member 62 and the bottom of the recess 74. The spring 75 biases the member 62 into abutment with a shoulder on the shaft, tending to move the shaft axially. A washer 76 and lock ring 77 are fastened on the end of the shaft at the Voutside of the casing to hold it in the casing. The spring 75 has a strip 78 extending across the center of the recess 74 and iitting in a channel 79 in the lower face of the polygonal member 62 to key the spring thereto. A detent S0 is provided on the outer edge of the spring to drop into a groove 81 in the recess 74 when the control 10 is adjusted to the off position. The user of the switch may thus determine by feel When the control is in the olf position. Additional grooves may be provided in the recess to locate various active positions of the adjusting cam.

The plate G has a portion 82 extending from the stack assembly on the side opposite the'recess 53 supporting the movable contacts 84 and 85 of the line switch 14 and the pilot light switch 16, respectively. The plate 58 has an arcuate opening or slot 83 formed therein adjacent the stack to permit the contact supporting portion 82 to dellect more easily. The plate portion 82 is bifurcated to permit thecontacts 84 and 85 to move relative each other when they engage stationary contacts 88 and 89 of switches 14 and 16, respectively. `A projection 90 on the plate is disposed to engage a second active surface 91 of the cam which opens the switches 14 and 16 when cam 6? is adjusted to the off position. The stationary contacts 88 and S9 of the line switch 14 and the pilot light switch 16 are attached to terminals 88a and 89a, respectively, extending through the casing.

In the off position of the cam 60 the projection 90 is biased downwardly into engagement with the cam surface 91 to keep the cam 6) bearing against the bosses 66 and 67. When the switches 14 and 16 are closed the projection 9G will be disposed to permit a small amount of play of the cam 69 between the projection and the bosses. ln all cam positions the spring arm 24 acts through the pin 54 and the boss 53a to hold the cam 66 against the boss 68 on the bimetal 7i) and keeps the latter seated in the channel 71.

This control may be connected, as shown in Fig. 3, to regulate the energization of an electrical resistance heater 92 from a conventional three-wire power source represented by conductors L1 and L2 and neutral N.

The operation of this control will be explained by referring to Fig. 3. When the cam is adjusted from the off position to a position other than its highest heat position, the cycling switch 12 and the line and pilot light switches 14 and 16 will be closed. Therheater 92 is connected in series with the storage bar heater 36 between the line switch 14 and the cycling switch 12, these switches serving to connect the main heater and bar heater to'conductors L1 and L2. The current in the bar heater 36 will cause the latter to gradually raise the temperature of the bar 34 and heat will be conducted therefrom to the bimetal 32. The latter will deflect downwardly upon being heated and the ceramic pin 39 will engage the resilient strip 28 to open the switch 12 by moving the cycling contact 26 away from the adjusted contact 22. When the circuit is broken at these contacts, both the main heater 92 and bar heater 36 are deenergized. However, heat that is stored in the bar will continue to flow to the'bimetal 32 and the latter will deflect further in contact separating direction so that the contacts 22 and 26 Vwill be distinctly separated without any fluttering. When the heat in the storage bar 34 and in the bimetal 32 is dissipated to the air therearound and to the stack assembly, the Vbimetal will cool and deflect in the opposite direction to permit the contacts of the cycling switch 12 to close. When these contacts close, the bar heater 36 will again be energized, but there is a time lag before the bar 34 is heated suillciently to conduct heat to the bimetal 32. Thus, the bimetal continues to cool and dellect in the contact closing direction even after the switch 12 is closed.

When the cam is adjusted to the highest heat position, the lowest portion 58a of the active surface 58 is engaged by the boss 53 on the plate. In this cam position the ceramic pin 54 will be disposed to allow the strip 24 to position the adjustable contact 22 in a lower position wherein the cycling contact cannot be separated therefrom by the bimetal 32 even when the bar heater is continuously energized and thus the heater 92 may be energized continuously.

VThe wattage control described above possesses an advantage in matching the switch to a load, such as a range surfacerheater, during warm-up periods. The warm-up time of the wattage control may be varied by changing the heatstorage characteristics or thermal mass of the heat conducting storage bar 34 which is made of brass or other metal in 'order to match it with the Warm-up time of the load. The total cycle time is governed primarily by the thermal conductivity of the storage bar. While the invention has been shown in but one form, it will be obvious to those skilled in the `art that it is not so limited, but issusceptible of various changes and modi- Atications without departing from the spirit thereof.

' What is claimed is: Y

1. A thermal cycling switch structure comprising a pair of relatively movable switch contacts and a pair of electrically conducting resilient arms supporting the contacts, fa first bimetal strip having a fixed end and a portion deectible upon heating and cooling of the strip to actuate one of said arms to respectively open and close the contacts, a heat storage bar of good heat conducting material having one end adjacent the tixed end of the bimetal strip in good heat conducting relationship therewith, the other end of the bar extending in spaced relationship with the bimetal strip, an electrical resistance heater supported in good heat transfer relationship with the latter end of the bar, means for connecting the heater in series with said contacts and an electrical load to be controlled by the contacts, each of the arms and the adjacent ends of the bar and strip being clamped together in stacked relationship, said `arms being electrically separated in the stack, a member engageable with the other `of said arms for adjusting the temperature of the bimetal strip at which said contacts are actuated, and means for adjusting said member comprising `a manually adjustable cam and a second bimetal strip, the cam providing adjustment of said switch to change the percentage of closed contact time during its cycling operation, the second bimetal strip adjusting said switch to compensate for changes in temperature ambient the rst bimetal strip, the deectible portion of said first bimetal strip being so constructed and arranged relative the heat storage bar as to separate the contacts primarily in response to heat conducted to the strip from saidV bar and to lag the temperature changes of said other end of the bar during heating and cooling thereof.

2. A thermally cycled switch structure comprising a switch having a pair of electrically conducting resilient strips and a pair of contacts carried by said strips, a first bimetal strip having a portion deflectible in response to heating and cooling to respectively open and close said contacts, a heat storage bar of good heat conducting material, `an electrical resistance heater in good heat transfer relationship with said bar, a tubular clamping member extending through each of said strips and said bar for clamping them in fixed relationship in a stack, said resilient strips being electrically insulated from each other in the stack, said bimetal strip and said bar being clamped in good heat conducting relationship in the stack, thev deectible portion of said bimetal being so constructed and arranged relative the heat storage bar as to lab it in temperature change during heating of the bar by the heater, and means supported in the stack for connecting the switch and the heater in series with an electrical load to be controlled by the switch, an adjustable shaft supported by the stack, and means including a member actuated by the shaft for adjusting the switch to change the percentage of closed contact time during the cycling operation thereof, said last-mentioned means including 1a second bimetal strip acting upon said member to compensate for temperature changes ambient the iirst bimetal strip.

3. A thermostatic switch structure comprising a switch having a pair of switch contacts, each of said contacts being supported by a resilient spring arm, `a bimetallic strip disposed to deflect upon being heated to actuate one of said spring arms to separate said contacts, means for clamping each of said spring arms and said bimetal in electrically insulated fixed relationship in a stack assembly, said clamping means including a tubular member extending through the stack assembly, a switch adjusting shaft extending through the tubular member and rotatable therein, said shaft having a portion extending from one end of said member for connection to shaft operating means, a rotatable cam coupled to said shaft, said cam having an active cam surface, a cam follower engaging said active surface and disposed to adjust the position of said other spring arm axially of said shaft in response to rotation of said cam by the shaft to adjust the temperature of said bimetallic strip at which said contacts are separated.

4. A thermostatic switch structure comprising a switch having a pair -of switch contacts, a pair of spring arms supporting said contacts, a bimetallic strip disposed to deflect upon being heated to actuate one of said spring arms to separate said contacts, means for clamping each of said spring arms and said bimetal in fixed relationship in a stack assembly, said arms being electrically insulated from each other in the stack, said clamping means including a tubular member extending through the stack assembly, a switch adjusting shaft extending through the tubular member and rotatable therein, said shaft having a portion extending from one end of said member for connection to shaft operating means, a rotatable cam coupled to said shaft, said cam having an active cam surface, a cam follower engaging said active surface and disposed to adjust the position of said other spring arm axially of said shaft in response to rotation of said cam by the shaft to adjust the temperature of said bimetallic strip at which said contacts are separated, a third contact carried by said structure, a movable contact engageable with said third contact, a resilient spring member carrying said movable contact and having a portion secured in said stack assembly, said cam having a second active surface, a cam follower engageable with said second active surface for actuating said movable contact relative said fixed contact.

5. A thermostatic switch structure comprising a switch having a pair of switch contacts, a pair of spring strips supporting said contacts, a bimetallic strip disposed to deflect upon being heated to actuate one of said spring strips to separate said contacts, means for clamping each of sai-d spring strips and said bimetal in 'fixed relationship in a stacl; assembly, said arms being electrically insulated from each other in the stack, said clamping means including a tubular member extending through the stack assembly, a switch adjusting shaft extending through the tubular member and rotatable therein, said shaft having a portion extending from one end of said member for connection to .shaft operating means, rotatable cam coupled to said shaft, said cam having an active cam surface, a cam follower engaging said active surface and disposed to adjust the position of said other spring strip axially of said shaft in response to rotation of said cam by the shaft to adjust the temperature of said bimetallic strip at which said contacts are separated, said cam being keyed to said shaft but axially movable relative thereto, and a thermally-responsive device for actuating said cam axially of .said shaft to adjust the temperature of said bimetallic strip at which said pair of contacts are separated.

6. A thermostatic switch structure comprising a switch having a pair of switch contacts, a pair of spring arms supporting said contacts, a bimetallic strip disposed to deflect upon being heated to actuate one of said spring arms to separate said contacts, means for clamping each of said spring arms and said bimetal in xed relationship in a stack assembly, said arms being electrically insulated from each other in the stack, said clamping means including a tubular member extending through the stack assembly, a switch adjusting shaft extending through the tubular member and rotatable therein, said shaft having a portion extending from one end of said member for connection to shaft operating means, a rotatable cam coupled to said shaft, said cam having an active cam surface, a cam follower engaging said active surface and disposed to adjust the position of said other spring arm axially of said shaft in response to rotation of said cam by the shaft to adjust the temperature of said bimetallic strip at which said contacts are separated, a thermallyresponsive device mechanically connected to said cam to adjust said other spring arm axially. of said shaft in response to a change in temperature sensed by said device to change the temperature of said bimetallic strip at which said contacts are separated.

7. A thermostatic switch structure comprising a switch having a pair of switch contacts, a pair of relatively movable electrically-conducting arms carrying said contacts,

asaanaa a bimetallic strip disposed to deflect upon being heated to actuate one of said arms to separate said contacts, means for clamping each of said arms and said bimetal in fixed relationship in a stack assembly in the structure, said arms being electrically insulated from each other in the stack, said clamping means including a tubular member extending through the stack assembly, a switch adjusting shaft extending through the tubular member and rotatable therein, said shaft having a portion extending from one end of said member for connection to shaft operating means, a rotatable earn coupled to said shaft, said cam having an active cam surface, a cam follower engaging said active surface and disposed to adjust the position of said other arm axially 'of said shaft in response to rotation of said cam by the shaft to adjust the temperature of said bimetallic strip at which said contacts are separated, said cam being keyed to said shaft but being axially movable relative thereto, said cam having a flat surface on the side opposite said active surface, fixed pivotal supporting means in said structure engaged by said cam at one side of said shaft, an adjustable support engaging said cam at the otherrsidecof said shaft, a thermally-responsive device for actuating said adjustable support to adjust said cam and said active surface axially of said shaft to change the temperature of said bimetallic strip at which said contacts are separated.

8. A thermostatic switch structure comprising a switch having a pair of switch contacts, a pair of electricallyconducting arms carrying said contacts, a bimetallic strip disposed to deflect upon being heated to actuate one of said arms to separate said contacts, means for clamping each of said arms and said bimetal in lixed relationship in a stack assembly, said arms being electrically insulated from each other in the stack', said clamping means including a tubular member extending through the stackrassembly, a switch adjusting shaft extending through the tubular member and rotatable therein, said shaft having a portion extending from one end of said member for connection to shaft operating means, a rotatable cam coupled to said shaft, said cam having an active cam surface, a cam follower engaging said active surface and disposed to adjust the position of said other arm axially of said shaft in response to rotation of said cam by the shaft to adjust the temperature of said bimetallic strip at which 8 Y said contacts are separated, an electrically insulating housing, a plate attached to said. housing and defining therewith a switch chamber, said switch stack assembly being securedV to said plate by said tubular member, and said switchbeing disposed within said chamber.

9. A thermostatic switch structure comprising a switch having a pairgof contacts, said contacts being carried by a paire-f relatively movable arms, a bimetallic strip detlectible for actuating one of said contacts to open and close said switch in response to heating and cooling thereof, said arms and said strip each having a portion clamped in a stack assembly, a housing for said stack, a removable closure for said housing, said closure having a portion clamped in said stack so that said stack and said closure form a unitary assembly, and means for manually adjusting the temperature of said strip at which said switch is actuated, said means including an adjustable member extending through said closure.

10. A thermal cycling switch structure comprising a switch having a pair of relatively movable contacts, said contacts being carried by a pair of electrically conducting strips, a bimetal strip deflectible upon heating and cooling to respectively open and close said switch, a heat storage bar of good heat conducting material, an electric heater clamped to said bar in good heat transfer relationship therewith, means for clamping each of said strips and said bar in lixedjrelationship in a stack, said resilient strips being electrically insulated from each other in said stack, said bimetal strip and said bar being clamped in good heat transfer relationship in the stack, a housing including a closure for enclosing said stack, said closure being in the form of a flat plate and being clamped in said stack so that the stack and closure form a unitary'assembly, and means extending outside said housing through said closure for manually adjusting the percentage of time the switch is closed during its cycling operation.

References Cited in the le of this patent UNITED STATES PATENTS c 2,235,893 Kuhn et al Mar. 25, 1941 2,567,138 Weiland Sept. 4, 1951 2,700,715 Peterson Jan. 25, 1955 2,768,263 Callihan Oct. 23, 1956

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