US2476083A - Thermostatic switch - Google Patents

Description

July 12, 1949. E. K. CLARK 2,476,033

' 'rmanuosm'rxc SWITCH Original Filed Jan. 9, 1942 3 Sheets-Sheet 1 /7 4/ 26 2 B/meI-a 2 Bimefa/ INVENTOR WiTNESS i I U F/G- 4- Ear/ K. C/ark E "-15 BY WW ATTOFNEY y 1949- E. K. CLARK 2. 476,083

THERMOSTATIC SWITCH Original Filed Jan. 9, 1942 3 Sheets-Sheet 2 WITNESSES: I ENVENTOR ZZ-/c7 M FIG. 8. Ear/K C/Ufk July 12, 1949. E. K. CLARK THERMOSTATIC SWITCH Original Filed Jan. 9, 1942 3 Sheets-Sheet 3 XEZZ WlTNESSES:

INVENTOR far/ K. Oar/r ATTORNEY J Patented July 12,1949

THERMOSTATIC SWITCH Earl K. Clark, Mansfield, Ohio, asslgnor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Division of application Serial No. 426,209, January 9, 1942. Continuation of application Serial No. 523,107, February 19, 1944. This application January 18, 1945, Serial No. 573,387

1 This invention relates to an electricallyheated appliance and particularly to a temperature control and indicating device for such an appliance, and it has for an object to provide an improved device of the character set forth. This application is a division of my copending application, Serial No. 426,209, filed January 9, 1942, now Patent No. 2,439,795, granted April 20, 1948, and is also a continuation of my application, Serial No. 523,107, filed February 19, 1944, which is now abandoned.

While the invention is particularly adapted for use with and has been illustrated and described as applied to an electrically-heated fiatiron, it will be apparent to those skilled in the art that its use is not limited to such application.

Flatirons and other electrically-heated appliances have been provided with a thermostatically-controlled switch for turning the heating element on and of! to maintain the appliance substantially at a desired temperature. Actually, the temperature rises and falls repeatedly within a limited range as the heating element is turned on and off. Such a thermostatically-controlled switch usually has provision for adjusting it to diilerent temperature settings.

Some flatirons have also been provided with an indicator light which is controlled by the same switch and, therefore, goes on and off simultaneously with the heating element. The purpose of the light is to indicate to the user when the iron is at a temperature suitable for use. For example, in the initial heating up of the iron from room temperature to the desired operating temperature, the light is on continuously along with the heating element. When the light goes out, the user knows that the iron has reached the desired temperature.

Such an indicating light, however, has certain limitations. as the heating element is energized intermittent- 1y to maintain the desired temperature range, and during such times the user has no indication that the iron is within the desired temperature range. Also, during the initial heating period, the light does not go out until the iron reaches a the set temperature at which the thermostatically-controlled switch opens its contacts, whereas the iron is ready for use when the temperature reaches the lower limit of the range maintained by the thermostat; in fact, it is usually suitable for use before then, since, for a given material to be ironed, a range of temperature greater than that maintained by the thermostat is suitable. Similarly, when the iron has been used at a rela- The light goes on again repeatedly Claims. (Cl. 200-138) tively high temperature and the thermostat is adjusted for a lower temperature, the user has no indication that the temperature has decreased to the lower desired temperature until the switch closes its contacts, which occurs at a temperature below the upper limit of the temperature range at which the iron is suitable for use.

It is an object of this invention to provide an indicator which tells the user when the iron is at a temperature suitable for use, regardless of whether the heating element is on or off.

A further object is to provide an indicator which gives an indication as soon as the iron reaches the range of temperature suitable for use without waiting for the temperature at .which the thermostatically-controlled switch turns the heating element on or ofl.

A further object is to provide an improved temperature control and indicating device for use with an electrically-heated appliance or the like which will automatically maintain the appliance within a predetermined temperature range and which also indicates when the temperature of the appliance is within that range or within a somewhat greater range of temperature which may be suitable for use; a more particular object being to provide such a device which may be adjusted to vary the predetermined temperature range as desired.

A further object is to provide an improved control and indicating device for use with an electrically-heated device or the like which will maintain the temperature of the appliance within a predetermined range and which gives a positive indication when the appliance is above or below said range, or at a slightly greater range which may be suitable for use, and which gives a different positive indication when the appliance is within such range of temperature.

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

Fig. 1 is a side elevation of an electricallyheated ilatiron embodying the present invention, a portion of the iron being broken away to show certain details of construction;

Fig. 2 is a side elevation of the temperature control and indicating device visible in Fig. 1, the supporting plate thereof being shown in longitudinal section, and the parts carried thereby being shown in the position they assume when I the iron is below the desired or set temperature Fig. 3 is a viewsimilar to Fig. 2 and includin! a wiring diagram of the electrical circuit employed in the iron illustrated in Fig. 1, the parts of the temperature control and indicating device being shown in the position they assume Just prior to the time when the thermostat reaches its set temperature;

Fig. 4 is a graph showing the variation in temperature of the temperature-responsive element of the present thermostat and also showing the temperature range in which the indicator light is on;

Fig. 5 is a plan view of the device illustrated in Figs. 2 and 3;

Fig. 6 is an end elevation looking from the right of Fig. 3;

Figs. 7 and 8 are plan and side elevation views, respectively, of a modified temperature control and indicating device which may be employed in the iron illustrated in Fig. 1, a schematic wiring diagram of the circuit employed with this form of the invention being shown in Fig. 8;

Fig. 9 is an end elevation of the device shown in Figs. 7 and 8, as viewed from the right of Fig. 8;

Fig. 10 is an enlarged detailed view of a portion of the device of Figs. 7 and 8, showing the relation of certain parts when the iron is below its set temperature;

Figs. 11 and 12 are plan and side elevation views, respectively, of another form of the invention, and which may be employed in the iron illustrated in Fig. 1, a schematic wiring diagram of the circuit employed with this device being shown in Fig. 12;

Figs. 13 and 14 are end and side elevation views, respectively, of one of the spring contact arms used in the device illustrated in'Figs. 11 and 12, as viewed from the left and from the front, re-

spectively of Fig. 11;

Figs. 15 and 16 are left end and front elevation views, respectively, of a spring, contact-carrying, arm and cooperating bimetal element used in the device illustrated in Figs. 11 and 12; and

Fig. 17 is a view of the device illustrated in Fig. 11, looking in the direction of the arrow A, the supporting plate being broken away along the line XV'IIXV'II of Fig. 11.

Referring to the drawings and particularly to Figs. 1 to 6, inclusive, there is illustrated an electrically-heated fiatiron generally indicated l8, which comprises an electrically-heated soleplate H, a, cover I8, and a handle IS. The soleplate may be heated in any conventional manner, as by a, resistance element clamped thereto or preferably by means of an armored resistance element cast or embedded therein. The resistance element for heating the soleplate is schematically indicated at 28 in Figs. 3, 8, and 12.

The resistance element 28, controlled by means of an adjustable thermostat, generally indicated 2|, supplies heat to the soleplate to maintain the same within a desired or set temperature range de ermined by the settting of the thermostat. The thermostat 2i is preferably supported within a recess in the soleplate II, as shown in Fig. 1, with its heat-responsive bimetal element 23 mounted closely adjacent the soleplate so that the bimetal element will be responsive to the temperature of the soleplate. The thermostat 2| controls a circuit for the heating element 28 of the iron and also controls a second circuit in such a manner that an incandescent lamp 28 or other electrically-operated visual or audible signal in the second circuit will indicate to the operator of the iron when the iron is within its set temperature range and therefore ready for use. The lamp or signal 26 may be mounted in any desired position on the iron, as for example, within the cover 18 below a window 21 (Fig. 1). I

Referring particularly to Figs. 2 and 3, where the thermostat 2| is shown apart from the iron, it will be noted that the thermostat structure is mounted on a supporting plate or base 28 which may be secured to posts 28 formed on or carried by the soleplate II. The plate 28 is provided with a depending post 3!, adjacent its rear end, to which the bimetal strip 23 is secured. This post also carries a spring, contact-carrying, arm 32 which is normally self-biased or sprung upwardly as shown in Fig. 2. The bimetal strip 23 and the arm 32 are preferably insulatedly mounted on the post 3| with the bimetal strip arranged to bow toward the arm when heated. .f

A contact 33 carried on the free end of the spring arm 32 is adapted to engage a cooperating contact 34 carried by a pivoted contact frame 35. These contacts, when closed, complete an energizing circuit (Fig. 3) for the heating element 28.

The contact frame 35 comprises an irregularly.- shaped rigid member which includes a horizontal portion 36 disposed above the base 28 and provided with depending flanges 31 having aligned V- shaped notches 31' therein. These flanges 31 are receivable in spaced apertures 38 (Figs. 5) formed in the base 28. The edges of the plate 28, at these apertures, which face the notches 31 in the flanges 31, are preferably beveled to provide fulcrum or pivot points receivable in the notches 31' so that the frame 35 is free to rock on the plate 28.

A vertical portion 48 of the frame 35 extending downwardly from the forward or left end of the horizontal portion 36 terminates in a U-shaped portion 4| which carries the mentioned contact 34 in the upper arm thereof. The lower arm of this U-shaped portion carries an insulating but-' ton or stop 42. The spacing between 'the upper surface of this button 42 and the contact 34 is preferably such as to provide a clearance for the movable contact 33 carried by the arm 32 of the order of between .005 and .018 inch. The contact 34 may be provided with a terminal arm 44, insulated from the frame 35, while a terminal 45 may be connected to the fixed end of the spring arm 32, for connecting the contacts 33 and 34 in the circuit for the heating element 28 (Fig. 3).

The vertical portion 48 of the contact frame 35 extends through an opening 28' formed in the base 28 and has connected thereto one end of a tension spring 46, the other end of this spring being anchored to the base as indicated at 41. The spring 46 normallymaintains the contact frame 35 in the position shown in Fig. 3.

A pair of spring, contact-carrying, arms 43 and 58 are insulatedly fixed to the base 28 as by means of a supporting post 5|. Contacts 52 and 53 carried by the arms 49 and 58, respectively, control a circuit (Fig. 3) for the signal lamp 26. A screw 54 adjustably threadedinto the horizontal portion 36 of the contact frame 35 is positioned with the head thereof, which is made of nonconducting material, between the projecting free ends of the spring arms 43 and 58* so that when the contact frame is materially above (Fig. 2) or below its normal position (Fig. 3), the screw head will engage one or the other of the arms 49 and 58 and separate the contacts 52 and 53 to interrupt the lamp circuit. From the construction just described it will be seen that the signal lamp circuit will be closed only when the contact frame is in or near its normal position.

The thermostat 2| is adjusted by means of a rod 55 which is threaded through the base 28 in alignment with the bimetal strip 23. The upper end of this rod has fixed thereto an operating knob 56 (Fig. 1) which may be provided with a suitable scale adapted to be read in conjunction with an index such as 51 and which may comprise a projection formed on the front support of the handle l9. This scale may he graduated in any desired manner to indicate the temperature of the soleplate either in degrees or types of material adapted to be ironed when the iron is at its set temperature. The lower end of this rod carries a button 58, of insulating material,

which is adapted to engage the bimetal strip 23 adjacent its fixed end so that on turning the knob 56 in one direction or the other, the bimetal strip will be moved closer to or further away from the spring arm 32.

The bimetal strip 23 is mounted on the post 3| so that an increase in temperature of the bimetal strip will cause it to bow downwardly. It will be understood that the rod 55 may be turned down sufficiently to maintain the contacts 33 and 34 open and thereby provide an off position for the iron without the need of aseparate line switch. When the iron is at room temperature and the thermostat adjusting knob 55 is turned from its off position to a position to maintain the iron at a particular temperature, the rod 55 is thereby raised, allowing the bimetal strip 23 to spring upwardly in a direction away from the spring arm 32. Since the spring arm 32 is self-biased upwardly, under the condition just mentioned this spring arm will also move upwardly and cause its contact 33 to engage the contact 34 carried by the contact frame 35 and raise the contact frame to substantially the position shown in Fig. 2. With the contact frame in this position, the head of the adjusting screw 54 has raised the upper springarm 49 and separated contacts 52 and 53 to interrupt the circuit for the indicating lamp 25 whilethe contacts 33 and 34 are closed and complete the circuit for energizing the heating element 25.

As the temperature of the soleplate increases, the temperature of the bimetal strip 23 also increases and it begins to bow downwardly and eventually its free end, which may be provided with a spherical knob 59, of insulating material, will engage the spring arm 32. Continued bowing of the bimetal strip forces the spring arm 32 downwardly until it reaches the position shown in Fig. 3. The spring 46 causes the contact frame to follow the spring 32 to maintain contacts 33 and 34 closed until this frame reaches its normal position (Fig. 3). When in this position, the contacts 52 and 53, which control the lamp circuit, have closed and further movement of the bimetal strip causes the contact 33 to move clear of the contact 34 and open the circuit for the heating element 20. From the above description, it will be seen that the signal lamp 26 will be energized prior to the interruption of the circuit for the heating element 20, and that this last-mentioned circuit is interrupted when the thermostat reaches its set temperature.

After the heater circuit has been interrupted by opening of contacts 33 and 35, the soleplate and the bimetal strip begin to cool, allowing the bimetal strip to move upwardly so that the con- 75 range, after which it follows a 8 tacts 33 and 34 will again close to energize the heating element 20 to maintain the soleplate within its set temperature range. It will be appreciated that when the soleplate is within its set temperature range the thermostat cycles between "01! and on" to open and close contacts 33 and 34 and intermittently energize the heater to maintain the temperature of soleplate within that range.

The movement of the bimetal strip 23 during this cycling operation of the thermostat is suificient to open and close contacts 33 and 34 but the clearance between the head of screw 54 and the projecting ends of the spring arms 43 and 50 is preferably such as to allow the contacts 52 and 53 to remain closed during such cycling of the thermostat so that the lamp 25 remains lit as long as the soleplate is within the set ternperature range. The clearance between the head of screw 54 and the projecting ends of the spring arm-s may be adjusted by means of a screw 54a which is adjustable in an offset portion of the upper spring arm 43 and engageable by the screw head.

To change the set temperature of the iron frame a previously high temperature to a lower temperature, as for example, when it is desired to iron with the soleplate at 250 F. and the iron is already at 350 F., the adjusting rod 55 is turned down causing the free end of the bimetal strip 23, which is already adjacent to the spring arm 32, to be flexed downwardly and move this arm so that its free end engages the insulating button 42 of the contact frame 35 and thereby swing the contact frame below its normal position (Fig. 3).

This movement of the contact frame 35 causes the head of the adjusting screw 54 to engage the free end of the lower spring arm 50 to pull it downwardly and open the contacts 52 and 53 and extinguish the lamp 26. With the lamp out the operator knows that the iron is no longer at the temperature indicated by'the scale on the thermostat adjusting knob 55. The mentioned movement of the spring arm 32 also opens the contacts 33 and 35 so that the circuit for the heating element 23 is interrupted and will remain open until the soleplate and the bimetal strip heated thereby have cooled sufficiently to allow the parts to move to the position shown in Fig. 3. As in the case where the iron is being brought up to heat, on allowing the iron to cool from a previous higher temperature to a new signal light 28 will be better understood by reierence to the graph of'Fig. 4, wherein the temperature of the bimetal element 23, which may also be considered as a measure of the soleplate temperature, has been plotted against time to show approximately the action of the switches 3334 and 52-53. It ,will be understood that the shape of the temperature curve will vary depending on the various characteristics of the iron, particularly the thermostat and its thermal relation to the soleplate and also depending on the conditions of use.

In this graph, time is' plotted on the abscissa, and temperature, of the bimetal, on the ordinate. The curve A represents the temperature of the bimetal element which, starting at room temperature, rises until it reaches the set temperature sinuous path throughout this range to approximately the ver- I spectively, the lower and upper limits of the light switch 5253, As long as the temperature of the bimetal element lies between these lines, with the thermostat set to maintain the 'iron within the range represented by the sinuous part of the curve and to the left of the line D, the light switch will remain closed. The actual set temperature of the thermostat is indicated by the line E, this line representing the temperature which the bimetal element opens and closes the switch 33--34 to control the energization of the iron heating element 26.

As mentioned, in plotting this graph, it is assumed that the iron has been at room temperature and then turned on to operate at a predetermined set temperature, indicatedby the line E. It is, of course, not possible to maintain the iron at one particular temperature; in practice the set temperature of the iron and of the bimetal 23 actually is a temperature range or zone lying between the tops of the peaks and the bot toms of the valleys of the sinuous part of the graph.

As the iron heats up, the temperature of the bimetal increases, as represented by the curve A, until the parts of the thermostat reach the position shown in Fig. 3 where the light-controlling switch 52-53 has closed to light lamp 2%, the closing of this switch being represented by the point llll in Fig. 4. However, the switch 33-36- 33-34 again closes, but since the temperature of the thermostat does not drop below the line B, which represents the lower limit at which the light switch 52-53 closed, the light switch does not open. The thermostat continues to cycle to open switch 33-34 at points 104 and I06 and close it at points I and I0 the light 26 remaining lit for the particular setting of the thermostat as long as the temperature of the thermostat remains between the lines B and C. If the temperature of the thermostat were to rise above the line C, the light would be extinguished,

for under this condition the bimetal element would engage the spring 32 and move the contact frame below its normal position (Fig. 3) and open the signal switch 52-53. It will be understood that the greater temperature differential or range of the light switch 52-53, represented by the zone between the lines B and C,

, as compared to the actual temperature of the bimetal strip, is due to the clearance between the head of screw 54 and the contact spring-s l9 and 50.

On heating up the iron from a lower temperature, such as room temperature, the first peak of the curve A'may go above the upper line C due to the thermal lag between the bimetal element and the heated soleplate, with the result that the signal light will go out until the temperature of the bimetal element drops below the line C. However, on subsequent cycles of the thermostat switch, as the iron becomes saturated with heat, the peaks and valleys of the sinuous curve will lie within the lines B and C. In my copending application, Serial No. 436,299, filed March 26, 1942, and now Patent No. 2,409,420, granted Oct. 15, 1946, and assigned to the assignee of the present application, there is disclosed a thermostat structure which prevents overheating of the soleplate and of the bimetal element on the initial heating-up period.

If the [thermostat be adjusted to maintain the soleplate at a higher temperature, the switch 33-36 will close and the light 26 will go out, since the bimetal strip will be raised clear of spring 32 causing the parts to assume substantially the position shown in Fig. 2. The temperature of the soleplate and of the thermostat increases and at the point we (Fig. 4) the light switch E2-53 closes to illuminate the lamp 2% and indicate to the operator that the iron has reached the new temperature range. The thermostat switch 333l opens when the temperature thereof reaches approximately the point 599. The thermostat continues to cycle in the same manner as that described for the lower temperature setting to maintain the soleplate at the new temperature level.

The bimetal element shown in Figs. 1 to e and.

than that at which they open. In such case, the

points H92, H93, and its would lie on one horizontal line and the points W8, W5, and it! would lie on a second and lower horizontal line.

Both lines, however, would be between the tops zone bounded by the lines B and of the peaks and the bottoms of the valleys of the sinuous part of the graph and within the In Figs. 7 to 10, inclusive, there is illustrated a slightly modified form of the invention in which two signal lamps are provided, one of which may give a red signal and the other a green signal. In this form of the invention, the red signal will be illuminated whenever the iron is plugged into the linebut is not within irts set temperature range and indicates to the operator of the iron that it is not ready for use. The green lamp will .be lit only when the soleplate is within its set or operating temperature range as determined by the setting of the heating element 20 in exactly the same manner as the thermostat 2|.

The thermostat 2la diflers from the thermostat 2| in that three spring, contact-carrying arms 66, 6!, and 62, the lower two of which correspond to the spring arms 48 and 50 o! the thermostat 2|, are insulatedly carried by a post 68 fixed to the base 28. The contacts carried by lower and middle arms 62 and 6!. controi a circuit for greenlamp 26 to energize this lamp when the iron is within its set temperature range. The contact carried by the middle or 17, providing a vertical portion 11 which terminotes in a substantially horizontal portion 18. This horizontal portion carries a contact button 18 (Fig. 16) which is adapted to cooperate with a motor arm 6| also cooperates with a contact carried by the upper arm 60 to control a circuit for red lamp 64 for energizing the same when the iron is either above or below the ironing or set temperature range. 1

The middle spring arm 6| is normally selfbiased downwardly into contact with the contact carried by the lower arm, as shown in Fig. 8, so that whenever the contact frame 35 is in or near its normal position (Fig. 8) the green lamp will be lit and the red lamp will be out.

The middle arm 6| extends beyond the ends of the upper and lower arms 60 and 62 and is adapted to be engaged by an upstanding bracket 65 attached to the free end of a strip 66 loosely pivoted at 61 on the upper :face of the base 28. As shown particularly in Figs. 8, 9, and 10, the strip 66 is provided with opposed downwardly extending lugs 68. The depending flanges 31 on contact frame 35 of the thermostat 2Ia are provided with outwardly-extending shoulders 69 which are adapted to engage the lower edge of tie lugs 68. It will be understood that whenever the contact frame 85 is rocked above or below its normal position (Fig. 8) the shoulders 69 will engage the lugs 68 to raise the member 66. In Fig. 10, the base 28, the contact frame 35, and the member 66 have been shown in the relative positions they assume with the com tact frame 85 raised by the spring member 32 to a point above its normal position. Whenever the contact frame 35 is above or below its normal position, that is, when the iron is not within its set or operating temperature range, the member 66 acting through its upstanding bracket 65 raises the middle or motor spring arm St to open the contacts of arms Iii and (i2 and thus extinguish the green lamp and close the contacts of arms 68 and iii to light the red light.

In Figs. 11 to 16, inclusive, there is shown another and preferred form of the invention. The

modified thermostat, generally indicated 2w,

comprises a base plate 28a on which is supported a bimetal strip 230.. The bimetal strip 23a is rockably mounted at one end on 2. depending insulating post 3|a fixed to the underside of the base plate. As shown in Figs. 11 and 12, the bimetal strip 23a is provided with an open-ended slot H of a size to loosely receive the depending post 3m and this slotted end is also provided with a rocker or humped portion 12 disposed between a flange of the depending post and a helical compression spring I3 encircling the post above washers 14. The washers l4 clamp a spring, contactcarrying, arm 32a to the lower end of the post. The arm 32a is electrically connected to the terminal i5 as by means of rivet '16 which secures the post and terminal to the base plate 28a. A sheet of mica interposed between the terminal and the base plate 28a insulates these parts. It is to be understood that the bimetal strips 23 and spring arms 32 of thermostats 2| and 2m may be mounted in the manner just described.

The free end of the spring arm 32a is bent upwardly, as shown particularly in Figs. 12, 16, and

contact button 8| to control an energizing circuit (Fig. 12) for the heater element 20 of the iron. The contact 8| is carried on the underside of a spring arm 82 which is fixed at one end to the upper surface oi the base plate 28a as by means of a rivet which also secures terminal 88.

The vertical portion 11 of the spring arm is provided with substantially rectangular opening 84 (Figs. 16 and 17) to receive the T-shaped end of the bimetal strip 23a so that as the bimetal strip flexes it will be guided along this opening. By reference to Figs. 15 and 17, it will be noted that the spring arm 32a is provided with a stop 86 which projects into the opening 84 whereby the bimetal strip 23a may have substantially point contact with the spring arm when heated sufficiently to bow the same downwardly into engagement with th spring arm.

The position of the bimetal strip 23a relative to the spring arm is manually adjusted by means of thermostat adjusting screw 55 which is threaded through the base 28a. It will be understood that this screw will be manipulated by means of a knob like that shown at 56 in Fig. 1. The screw 55 is provided with a stop 86 (Fig. 11) which is adapted to engage a pin 86a carried by the base plate 28a when the thermostat is turned to its off position or to its extreme high position.

From the foregoing description, it will be understood that by raising or lowering the thermostat adjusting screw 55 to increase or decrease, respectively, the set temperature of the iron, the bimetal strip 23a will pivotin a vertical plane on its rocker portion 18. As inthe case of the previously described thermostats 2i and Zia, the bimetal strip 28a bows downwardly as its tem perature increases and eventually engages the stop carried by the spring arm. When the bimetal strip engages this stop, it moves the spring arm 32a downwardly allowing the spring arm 82 to be lowered until its free end 820. rests on the upper surface of the base 28a. Continued movement of the bimetal strip 23a causes the contact 18 carried by the spring arm 32a to be moved clear of the contact 85 to open the circuit for the heater 28. It will be understood that the thermostat Zib is calibrated to open these contacts when the temperature of the bimetal strip reaches the set temperature range of the iron as indicated by the scale carried by its adjusting knob.

The spring arm 82 carries a second contact 81 adjacent its free end which cooperates with a contact 88 carried by a third spring arm 89 (Figs. 11, 13, and 14) mounted on the under surface of the base 28a. The contacts 81 and 88 control a circuit for signal lamp 26 and are closed only when the iron is near its set temperature range.

By reference to Fig. 12 wherein the parts are shown in the relation they assume when the iron is below its set temperature range, it will be noted that the spring arm 32a holds the contact 81 up and away from the lower contact 88. As the spring arm 32a moves downwardly under the influence of the bimetal strip 23a these contacts will close, just prior to the time the contacts 19 and 8i open, to energize the lamp 26.

The lower spring arm 89 is fixed at one end to the base 28a by means of a rivet which also secures terminal 90. As shown in Figs. 13 and 14, this arm is provided with an ofiset horizontal portion 9i which is adapted to be engaged by the lower end of a screw 92 adjustably secured in a bracket 93 (Fig. 16) insulatedly attached to the horizontal portion 18 or the spring arm 32a. In the event the iron becomes too hot, that is, its temperature exceeds the set temperature of the thermostat or if the setting of the thermostat is decreased from a previous higher value, the bimetal strip 23a will move the spring arm 32a downwardly and cause the screw 92 to engage the horizontal offset portion 9| (Fig. 13) and thereby move the lower contact 88 away from the upper contact 81 to open the lamp circuit. This movement of the spring arm 32a also opens the contacts I9 and Si which control the heating element circuit.

The mentioned heating element circuit may be traced from one side of the line through the heating element 20, terminal I5, rivet I6, and arm 32a to the closed contacts 19 and 8!, spring arm 82, terminal 83 to the other side of the line. The mentioned lamp circuit may be traced from one side of the line through lamp 28, terminal 90, lower spring arm 89, closed contacts 88 and 81, spring arm 82 and terminal 83 to the other side of the line. Y

As in the case of the previously described thermostats 2i and Ila, while the thermostat lib is cycling to intermittently energize the heating element to maintain the iron or other appliance, controlled by the thermostat, within a predetermined temperature range, the lamp circuit, controlled by contacts 81 and 88, may remain closed in order to illuminate the lamp 26.

The operation of the thermostats Zia and 2lb is similar to the thermostat 2i and is represented by a graph similar to that shown in Fig. 4. However, in the case of the thermostat 2ia, the red light 64 will be lit whenever the green light 26 is out to give a positive indication that the iron is not at its set temperature.

While I have shown my invention in several forms, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications without departing from the spirit thereof, and I desire, therefore, that only such limitations shall be placed thereupon as are specifically set forth in the appended claims.

What I claim is:

1. A thermostat comprising a support, a temperature-responsive element carried by said support, an arm supported in a position to be moved 2 arm being biased toward said bimetal strip, a

member, having a contactthereon, supported on said base and biased to a predetermined .position, a contact carried by said arm and adapted to engage the contact carried by said member, said arm being adapted to displace said member from said predetermined position, said bimetal strip, when heated, being adapted to flex toward said arm to move the same in a direction away from said member to permit said member to return to said' predetermined position and to separate said contacts, a second contact carried by said member, and a second member supported on said base and having a contact thereon adapted toengage said last-mentioned contact when said first-mentioned member is in said predetermined position. 7

3. A thermostat comprising a support, a bi-' metal strip carried by said support, an arm supported in a position to be moved by said bimetal strip as said strip approaches a predetermined temperature, a contact member having a contact thereon. means for resiliently maintaining said contact member in a predetermined position, a contact carried by said arm in a position to engage said first-mentioned contact, said arm being adapted to move said contact member away from said predetermined position, said bimetal strip being adapted to move said am to move said second-mentioned contact clear of said first-mentioned contact and permit said contact-carrying member to be restored to saidv predetermined position, a' pair of contacts carried by said support, and means carried by said contact member for separating said last-mentioned pair of contacts when said contact member is held away from said predetermined position by said arm.

4. A thermostat comprising a support, a temperature-responsive element carried by said supby said element as said element approaches a predetermined temperature, a contact-carrying member movably supported on said support and biased to a predetermined position relative to said support, a contact carried by said member, a contact carried by said arm in a position to engage said first-mentioned contact, said arm being biased to displace said contact-carrying member from said predate Tm. ed position, said temperature-responsive element being adapted to move said arm away from said member to move said second-mentioned contact clear of said first-mentioned contact and permit said contactcarrying member to be restored to said predetermined position, and a switch carried by said support, said switch being actuated by said contact-carrying member upon movement thereof into and out of said predetermined position.

2. A thermostat comprising a base, a bimetal strip supported at one end on said base, an arm supported at one end on said base and extending substantially parallel to said bimetal strip, said port, an arm supported in a position to be moved by said element as said element approaches a predetermined temperature, a first member supported by said support and biased to a predetermined position relative to said support, first and second contacts carried by said member, a contact carried by said arm in a position to engage said first contact and move said member out of said predetermined position, a second member supported by said support and biased to a predetermined position relative to said support, said second member having a contact thereon adapted to engage said'second contact on said member when said member is in said predetermined position, said temperature-responsive element being adapted to move said arm away from said first member as said element approaches a predetermined temperature and thereby separate the contact carried by said arm from first contact and to permit said first member to be restored to said predetermined position, said contact carried by said second member engaging said second contact on said first member on restoration of said first member to its predetermined position.

5. A thermostat comprising a support, a ternperature-responsive element supported at one end on said support, an arm supported at one end on said support and extending substantially parallel '13 said predetermined position, said temperatureresponsive element being adapted, when heated, to flex toward said arm to move the same in a direction away from said member to separate said contacts and permit said member to return to said predetermined position, a second contact carried by said member, and a contact adapted to engage said last-mentioned contact when said member is in said predetermined position.

6. A thermostat comprising a support, a contact-carrying member mounted on said support and biased in contact-closing direction to a predetermined position relative to said support, a contact carried by said member, an arm mounted on said support, a contact carried by said arm in a position to engage the first-mentioned contact, temperature-responsive means for controlling movement of said arm, and a switch adapted to be actuated by said contact-carrying member, said contact arm being operable upon change in temperature in one direction to move the contact carried thereby into engagement with the firstmentioned contact and then to move said contact and said contact-carrying member in opposition to said bias, said contact-carrying member being operable to open said switch during such movement, whereby said switch is always opened at a temperature which is in the same relation to the temperature at which the contacts engage.

'7. A thermostat comprising a support, a contact-carryin member mounted on said support and biased in contact-closing direction to a predetermined position relative to said support, a contact carried by said member, an arm mounted on said support, a contact carried by said arm in a position to engage the first-mentioned contact, a switch adapted to be actuated by said contactcarrying member, a temperature-responsive element for controlling movement of said arm, said temperature-responsive element upon change in temperature in one direction causing said arm to move the contact carried thereby into engagement with the first-mentioned contact and then to move said contact and said contact-carrying member in opposition to said bias, the contactcarrying member being operable to open said switch during such movement so that the switch is always opened upon further change in temperature after said contacts engage, and means for effecting relative adjustment between said temperature-responsive element and said support to simultaneously vary the temperatures at which said contacts engage and said switch opens while maintainin said temperatures in substantially the same relation to each other.

8. A thermostat comprising a support, a pair of cooperating main contacts, a first arm carryingone of said main contacts, a pair. of cooperating auxiliary contacts, a second arm carrying one of said auxiliary contacts, each of said arms being biased in contact-closing direction, temperature-responsive means operable in response to increase in temperature to move said first arm to open said main contacts, said first arm being operable to actuate said second arm against the bias thereon to open said auxiliary contacts upon a predetermined increase in temperature after opening of said m'ain contacts, and adjusting means operable to vary concurrently the temperatures at which said main and said auxiliary contacts are opened.

9. A thermostat comprising a support, a pair of cooperating main contacts, a first arm carrying one of said main contacts, a pair of cooperating auxiliary contacts, a second arm carrying one of said auxiliary contacts, each of said arms being biased in contact-closing direction, temperature-responsive means operable in response to increase in temperature to move said first arm to open said main contacts, said first arm being operable to actuate said second arm against the bias thereon to open said auxiliary contacts upon a predetermined movement in contact-opening direction after opening said main contacts, there being a lost motion between said first and second arms so that the temperature may increase through a limited range, after opening of the main contacts, before opening the auxiliary contacts, and adjusting means operable to vary concurrently the temperatures at which said main and said auxiliary contacts are opened.

10. A thermostat comprising a support, a pair of cooperating main contacts, a first arm carrying one of said main contacts, a pair of cooperating auxiliary contacts, a second arm carrying one of said auxiliary contacts and biased in contact-closing direction, temperature-responsive means for actuating said first arm and effecting movement thereof to open said main contacts in response to increase in temperature and to close said main contacts in response to decrease in temperature, said first arm being operable to actuate said second arm against the bias thereon to open said auxiliary contacts upon a predetermined movement in contact-opening direction after openin said main contacts, there being a lost motion between said first and second arms so that the temperature may increase through a limited range, after opening of the main contacts, before opening the auxiliary contacts, and means for adjusting the relation of said temperature-responsive means and said first arm, thereby to vary concurrently the temperatures at which said main and said auxiliary contacts are opened.

EARL K. CLARK. REFERENCES CITED The following references are of record in the.

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