US2275893A - Control device - Google Patents

Description

March 10, 1942. w, J ETTlNGER 2,275,893

CONTROL DEVICE v F'ile'd April 17, 1940 His Attorneg Patented Mar. 10, 1942 CONTROL DEVICE Wallace J. Ettinxer, Chicago, lll., mignon' to Edison General Electric Appliance Company, Inc., Chicago, Ill., a corporation o New York Application April 17, 1 940, Serial No. 330,085

(Cl. o- 139) 12 Claims.

My invention relates to a control device and more particularly to a temperature responsive control device for controlling a heating circuit or the controlling circuit for a heating circuit, and has for its object the provision of a new and improved control device which is rugged in construction and may be manufactured at low cost.

More specifically, my invention relates to temperature control devices of the type described and claimed in United States Patent 2,128,869, granted August 30, 1939, on an application illed by Russell A. Winborne, and has for its object the provision of a new and improved arrangement lor obtaining diierent temperature settings over a wide range in a control device of this type. Brley, the Wlnborne patent discloses a control device ln which the thermally responsive element comprises two pieces of bimetal reversely` arranged and connected together at one end. Such an arrangement produces what is called a compound olmetal blade structure in which one portion of the blade movesln a direction opposite to the remaining portion in response to temperature changes. As described in detail in the Winborne patent, this construction is particularly effective in compensating :for what is termed temperature overshoot, l. e. the tendency of the control device to cut 'or at a higher temperature during the rst cycle of operation than during the remaining cycles due to the more rapid rise of temperature in the heated body than ln the control device.

It has been found that when such compound blades are used` in a control device, lower stress conditions are encountered in the blxnetal blade element. In accordance with my invention, full advantage is taken of this stress reduction in the provision of improved means for obtaining a temperature range in the control device. In particular, I have found that the reduced stress in the blmetal blade makes it possible to employ means bearing directly against the compound blade for obtaining temperature adjustment.

It is therefore a speclnc object of my invention to provide slmpliiled and improved means for adjusting the temperature of a control device employing a compound bimetallic blade, the improved means including an element which bears directly against the blmetallic blade.

It ls a further object of my invention to provide improved means for pivotaliy supporting the end of the compound bimetal blade, the pivotal supporting means being constructed and arranged so that by its action the compound blade the bimetal blade and for a given thickness of blmetal produces better contact pressure between the electrical contacts of the control device.

Further objects and advantages of my invention will become apparent as the :following description proceeds and the features of. novelty which characterize my invention will be set forth in the claims appended to and forming a part of this speclilcation.

For a more complete understanding of my invention. reference should be had to the accompanying drawing in which Fig. l is an elevation, partly in section, ci a ilatlron to which my improved control device has been applied; Fig. 2 ls an enlarged elevation, partly in section, showing detalls or construction of my improved control device; Fig. 3 is a view similar to Fig. 2 showing the control device in a dltlerent controlling posltion; and Fig. is an enlarged top view of my improved control device.

Referring to the drawing, l have shown my improved control device applied to control the heating circuit ci an electric latiron having a sole plate ill, a shell ll, a handle l2, and a heel stand i3.. Cast in the sole plate l@ is a heating unit lf3 which is preferably of the sheathed wire type such as ls described and claimed in United States Patent 11,367,342, granted February l, 1921, on an application flied by C. C. Abbott. Brleiiy, this heating unit comprises a coil of suitable resistance material it embedded in a mass of heat refractory electrically insulating material iS, such as magnesium oxide, the whole being enclosed by a metallic sheath Il. It is to be understood that an electric iron is shown merely for the purposes of illustration and control devices embodying my invention may be applied to control the heating circuit or the control circuit for the heating circuit, other heating appliances such as electric ranges, wallie irons. and-the like.

Referring now to Figs. 2 and 4, it will be observed that my improved control device comprises a. frame Il upon which all of the elements of my improved control device are mounted so as to produce a unitary structure which is secured in good thermal relation with the sole plate III` by a pair of screws I8, only one of which is ls stiflened thereby permitting the use o! thinner u material which results in still lower stresses in shown. Included in the trame l! is a danse 20 to which a temperature responsive element 2| is secured by means of rivets 22. An opening 2l is provided in the adjacent side wall 24 of the frame and the element 2l extends through this opening longitudinally oithe frame. As previously described, this temperature responsive element is a compound blmetal blade structure and comprisesr,

two relatively thin strips of bimetal 2Ia and 2lb downwardly. As described in detail in the aforementioned Winborne patent, such a construction is particularly effective in compensating for temperature overshoot.

Secured to the free or movable end of the compoundI blade 2I by means of a rivet 26 and insulated from the blade and rivet by means of mica strip 21 is a movable contact structure i which comprises a substantially U-shaped frame 28 on which is supported a bridging contact plate 29 consisting of a strip 30 of precious metal, such as silver, welded or` otherwise secured to a strip 3I of base metal, such as steel. This bridging contact plate is arranged to engage a pair of fixed contacts 32 which are mounted on a plate 33 of some suitable insulating material, such as mica, which in turn is secured by means of rivets 34 to the top wall of the frame IB. Suitable leads 35 are provided for connecting the control device in the electrical circuit to be controlled. In the electric flatiron illustrated, for example, one of the leads 35 is connected to the terminal 36 and the other lead is connected to one end of the heating unit I4, the opposite end of the heating unit being connected through a separate lead to the second terminal 38 to complete the electrical circuit.

As will be readily understood, movement of the compound blade in response to temperature changes will cause movement of the bridging contact to effect a controlling function. In order to cause this controlling function to take place quickly and with a snap action thereby eliminating chattering and burning of the contacts, a resilient member is provided which is pivotally mounted between a fixed substantially rigid support and the free end of the compound blade. The resilient member comprises a U-shaped spring 31 having bifurcated legs 38 and 39. Provided near the end of each portion of the leg 38 is a V-shaped notch 40 and provided near the end of each portion of the leg 39 is a similar notch 4I In order to provide a pivotal connection between the free end of the compound blade and the leg portion 38 of the U-spring a T-shaped plate 42 (see Fig. 4) is secured to the free end of the blade by the rivet 26. The head of this plate is arranged Ato extend across the blade ZI beyond the end thereof and a knife edge 43 is provided in the head on each side of the blade 2|. The knife edges 43 are inserted in the notches 40 provided on the legs of the U-spring so as to form a pivoted connection between the movable end of the compound blade and the U-sprlng,

In order to form a fixed pivot for the opposite end of the U-spring 31, a pair of downwardly extending substantially rigid arms 44 are pressed ation of the control device. of the U-spring positioned in the manner defixed knife edges illustrated in order to provide means for adjusting the thrust exerted by the U-spring 31.

Under the influence of U-spring 31, the free end of the compound blade is adapted to be moved with a snap action between two limiting positions. The fixed contacts 32 forms the limit for upward movement of the blade. Downward movement of the blade is limited by a stop which consists of an adjusting screw 46 threadedly mounted in an inwardly extending flange portion 41 of the frame I3 and having a rounded end 48 which engages the T-shaped plate 43 secured to the under side of the compound blade. When the screw 46 is adjusted to the proper height, it is locked in position by means of the nut 49. It will be noted that one of the limiting positions corresponds to the position when the bridging contact plate is in engagement with the fixed contacts to close the electrical circuit being controlled as shown in Fig. 2 and the other corresponds to the position when the bridging contact is separated from the fixed contacts to open the electrical circuit as shown in Fig. 3.

As described above, the fixed pivot for the U- spring is arranged so as to lie intermediate the ends of the bimetal blade 2|. It has been found that the operating characteristics of my improved control device are influenced considerably by the thickness of the bimetal used in the compound blade and it is desirable to use as thin a material as practicable in order to reduce the possibility of overstressing the blade during oper- With the fixed pivot scribedabove, the U-spring exerts an outward thrust on the compound blade which tends to stretch and stiffen the blade. This action of the U-spring permits the use of considerably thinner bimetal material than is the case when the fixed pivot is located beyond the free end of the blade and hence improves the operating characteristics of the control device.

As shown in Figs. 2 and 3, the movable pivot for the U-spring is located to the right of a vertical line through the movable and fixed contact members 28 and 32. It is apparent that this movable pivot could be located either to the right or tothe left of this vertical line. However, it has been found that the location of the movable pivot with reference to the end of the compound blade 2| has an appreciable effect on the action of the blade due to the change in effect of the vertical component of force exerted on the blade by the U-spring 31. In particular, it has been found that if the movable pivot is located to the left of the vertical line through the fixed and movable contacts and hence to the left of the end of the compound blade, the vertical component of force exerted by the U-spring on the blade tends to oppose its action, while if the movable pivot is located to the right of the vertical line through the fixed and movable contacts and hence beyond the end of the compound blade, the vertical component of force exerted by the U- spring will assist the action of the compound blade. For best thermostatic action with a thin, resilient, bimetal blade such as described above, it is important that the movable pivot be positioned so that the U-spring assists the action of the blade and for this reason the pivot is located to the right or a small distance beyond the vertical line through the xed and movable contacts.

In order to control the temperature at which the control device operates I have provided in `accordance with my invention a new and improved adjusting means whereby a range of temperature settings may be obtained varying from gage and bear against the upper surface of the bimetallic strip 2Ia. By means of the adjusting screw, the net force exerted bythe spring 31 may be controlled so that a greater or less force must be stored up in the bimetal blade due to its movement in response to thermal changes in order to cause the free end` of the bimetal blade to be moved from the closed to the opened position or from the opened to the closed position. For example, with the free end of the adjusting screw in the position shown in Fig. 2 which ishthe upper limit of its adjustment, substantially zero force is exerted on the compound blade by the adjusting screw and the contact pressure between the xed and movable contacts is a maximum, being the full value of the vertically upward component of force exerted on the plate 42 by the spring 31. Under these circumstances the bimetal blade sections must store up a maximum amount of energy in order to overcome this maximum initial contact pressure and to cause snap action movement of the movable contact to the opened position. However, when the adjusting screw 5D is rotated in a clockwise direction so as to move the end 5I thereof downwardly against the bimetal strip 2Ia, a vertical force is applied to the compound bimetal blade which acts against the upward vertical component of force exerted by the spring 31 so that the storing up of a smaller amount of energy will overcome the initial contact pressure and cause the movable contact to be snapped to the opened position. This means that a lower temperature will be maintained inthe appliance being controlled.

The range of my improved temperature adjusting means is regulated so that when the adjusting screw is rotated in the clockwise direction to an extreme position, the downward component of force exerted by the end of the adjusting screwon the compound blade will be sufficient to overcome completely the upward component of force exerted by the spring 31 and will cause the contacts to be snapped open thereby producing an oil position of the switch at normal or room temperatures.

Provided on the adjusting screw intermediate its ends is a knurled portion 52 upon which is mounted a washer 53 having an outwardly extending ear 54. This ear 54 vis adapted to engage an upwardly extending tang 55 provided on the frame I8 to limit the rotation` of the adjusting screw in both directions. If the adjusting screw is rotated clockwise until the ear 54 engages the front edge of the tang as shown in Fig. 2, the maximum temperature setting of the control device is obtained. If the adjusting screw is rotated clockwise until the ear 54 engages the opposite or back edge of the tang 55 as shown in Fig. 3, the minimum temperature setting is obtained which in my improved control is an off position for the electrical contacts.

As shown in Fig. l, the adjusting screw is adapted to extend upwardly above the top wall 51 adapted to cooperate with suitable indicia (not shown) on the top wall of the casing to indicate the temperature'for which the control device is set to operate as is well known in the art.

In order to maintain the adjusting screw at a particular setting within its range and to take up any looseness in the threads on the adjusting screw and the frame I8, a spring 58 is provided which lies between the top of the frame I8 and a shoulder 59 provided on the adjusting screw 50. As shown in Figs. 2 and 4, the spring 51 comprises a substantially flat U-shaped member, the leg portions of which engage the top of the frame I8 and the top of which is provided with av pair of arms 60 which engage the under surface of the shoulder 59. By means of this flat spring arrangement, the adjusting screw is biased upwardlyand is frictionally held in any position throughout its range of adjustment.

Considering the operation of my improved control device, it will be assumed for the purposes of explanation that the elements of the control device are in the position shown in Fig. 2. It will be observed that the adjusting screw has been rotated counterclockwise until the ear 54 engages the tang 55. Thisv produces the maximum temperature setting for the control and, under these circumstances, the end of the adjusting screw will exert little or no force on the compound bimetal blade element and consequently the upward force component of the U- spring 31 will be unopposed and the contact pressure between the fixed and movable contacts will be maximum. With the contacts closed as illustrated, the heating circuit for the iron will be energized. As the temperature of the sole plate of the iron increases, heat is transmitted by conduction to the portion 2Ia of the temperature responsive element. Heating of this portion of the temperature responsive element causes its free en'd to tend to deflect downwardly, the end of the adjusting screw serving as a fulcrum about which the deflection takes place. The portion 2 Ib heats more slowly than the portion 2|a and its effecten the operation of the control will be more fully described hereinafter. Due to the upward force exerted on the end of the temperature responsive element by the U- spring, no actual deflection of the section Zia will take place but energy will be stored in the section which tends to overcome the initial contact pressure between the contacts. When the device being controlled approaches the temperature for which the control device has been set to operate, enough energy will have vbeen stored in the, thin resilient bimetal strip to overcome the initial contact pressure produced by the vertical component of force of the spring 31 and the free end ofthe portion 2Ia of the bimetal strip will start to deflect downwardly.- As this downward deflection increases, the upward force exerted bythe spring 31 decreases and hence the bimetal blade will accelerate and will move rapidly and with a snap action in the downward direction until its movement is limited by the stop 46. As is well known in the art, the U- spring 31 functions to resist movement of the bimetal element up to a certain point and, once of the casing II ol the natiron and this upper end is provided with a knob 58 having a pointer movement is initiated, the U-spring functions to assist this movement until further movement is prevented by some fixed stop.

When the bimetal blade has been snapped against th'e fixed stop 46, the movable contact will have been moved away from the fixed contacts to open the heating circuit of the electric iron. The temperature of the iron and the section Zla will then start to decrease and this decrease in temperature will tend to cause an upward deflection of the bimetal section against the downward component of force exerted by the U- spring 31.` When the sole plate has attained a predetermined minimum temperature, sufficient energy will have been stored in the section Zia to initiate movement of its free end against the restraining force of the U-spring 31. Once movel ment vhas started, the restraining force of the U- screw which has the effect of varying the initial l contact pressure between the contacts of the control device so that a greater or lesser amount of energy must be stored in the bimetal blade to overcome this contact pressure. In the lower lim- -it of adjustment of the adjusting screw, the force exerted on the bimetal blade by the fulcrum end of the adjusting screw is sufficient to overcome the initial contact pressure and to initiate downward movement of the movable contact which results in the contact being snapped open producing amanually'fsettable off position. The force applied to the blade in this limiting position of the adjusting screwsis sufficient to hold the switch open for all normal temperatures, such as room temperature or temperatures slightly lower than room temperature. Y

The manner inwhich' the compound bimetal blade element functions to prevent temperature overshoot of the appliance during the first cycle of operation of the control device is clearly set forth in the aforementioned Wlnborne patent. It

' may be stated briefly that the compound blade compensates for the length of time required for the heat to travel from the fixed end of the bimetal element to the movable end thereof. For example, with the customary single length of bimetal, the bimetal continues to heat after the contacts have been open and thus the reclosing of the contacts for the second cycle is delayed. In addition, the bimetal blade reaches a saturated condition resulting in a lower temperature being maintained in the second and succeeding cycles than in the first cycle of operation. With'- the compound blade construction, however, the portion 2 Ib instead of deiiecting in a direction which would delay reclosing of the contacts after the first cycle of operation actually defiects upwardly in response to heat transmitted by conduction from the relatively higher temperature section Ila. Thus section 2lb is acting in conjunction with section Zia to produce a quicker or premature closing of thecontrol contacts on thesecond cycle. Moreover, after the compound blade saturates, the portion 2lb acting reversely to the Y portion Zia will delay somewhat the opening of the contacts during the second cycle. This premature closing of the contacts and the delayed opening thereof combine to elevate the maximum cut-ofi' temperature of the second cycle as well as the minimum temperature of the first cycle at which heat is reapplled. As a result, the

sole plate attains substantially the same temperature in succeeding cycles as in the first cycle of operation and temperature overshoot of the first cycle relative to the remaining cycle is substantially eliminated.

From the foregoing it will be observed that I have provided a control device which is simple in construction, is provided with novel means for pivotally supporting the free end of the temperature responsive member and is provided with a new and improved construction and arrangement for obtaining a temperature range 'of operation varying from a manually settable ofl position at normal or room temperatures to a predetermined high temperature setting.'

While I have shown a particular embodiment of my invention, lt will be understood, of course, that I do not wish to be limited thereto since many modifications may be made, and I, therefore contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. I n a temperature control device, a rigid supporting frame, a relatively thin compound bimetal blade element having one end fixed to said frame and its opposite end free to move, a resilient member for causing said bimetal blade to be moved quickly and with a snap action, means 'for pivotally mounting one end of said resilient member on said bimetal blade, relatively rigid means extending downwardly from said frame for pivotally supporting the opposite end of said resilient member, said last mentioned means being constructed and arranged so that said resilient member exerts a longitudinal force on said blade tending to stiften said blade, and control means associated with said blade so as to perform a controlling function in accordance with the snap action movement thereof.

2. In a temperature control device, a rigid support, a relatively thin compound bimetal blade element having one end fixed to said support and its oppositel end free to move, a resilient member for causing said bimetal element to be moved quickly and with a snap action, means secured to the free end of said bimetal element for pivotally mounting one end of said resilient member adjacent the free end of said blade, substantially rigid means extending from said support for pivotally supporting the opposite end of said resilient member so that said resilient member exerts a longitudinal thrust on said blade tending to stiien said blade, and control means associated with said bimetal blade so as to perform a controlling function in accordance with the snap action movement of said blade.

3. In a temperature control device, a rigid support, a relatively thin, resilient, compound bimetal blade element having one end fixed to said support and its opposite end free to move, control means associated with sald blade element and adapted to be actuated thereby to perform a controlling function, a resilient member pivotally mounted on said free end of said blade element and a fixed pivot so as to cause said blade element to be moved quickly and with a snap action, said fixed pivot lying intermediate the fixed and movable ends of said bimetal element so that said resilient member exerts a longitudinal thrust on said nember tending to stiften the same.

4. In a temperature control device, a rigid frame, a compound bimetallic element having one end secured to said frame and its opposite end free to move, control means associated with said free end and adapted to perform a' controlling function in accordance with movement thereof, resilient means for effecting movement of said bimetal element and said control means quickly and with a snap action, means for pivotally mounting said resilient means on the free end of said element, and relatively rigid-means for pivotally mounting said resilient means von said frame, said last mentioned means lying intermediate said fixed end and said movable end of said bimetallic element so that an outward force is applied longitudinally thereof.

5. In a temperature control device, a rigid support, a relatively thin, resilient, compound bimetal blade element having one end fixed to said support and its opposite end free to move, control means .associated with said blade element and adapted to be actuated thereby to perform a controlling function, a resilient member for causing said blade element to be moved quickly and with a snap action, rigid arms extending downwardly from said support on opposite sides of said bimetal element, said arms lying intermediate the fixed and movable ends of said bimetal element,

and means for pivotally mounting said resilient member between said arms and said free end of said blade element so that a longitudinal thrust is applied to said blade element which is adapted to stiffen said element.

6. In a temperature control device, a rigid frame, a relatively thin, resilient, compound bimetal blade element fixed at one end to said frame and having its opposite end free'to move in accordance with temperature changes, consaid thin, resilient bimetal element in order to,

stiffen the same.

7. In a temperature control device, a temperature responsive element'fixed at one end and having its opposite end free to move, said element comprising two sections of bimetal connected together at one of their ends so as 4to have the high expanding side of one section lying on the opposite side with respect to the high expanding side of the second section, control means associatedlwith said temperature responsive element and adapted to be actuated in accordance with movement thereof in response to temperature changes, a plate secured to the free end of said temperature responsive element having knife edges along one edge thereof, fixed arms extending downwardly on opposite sides of said temperature responsive element intermediate the fixed and free ends of said element, and a U- shaped spring for causing` said temperature responsive element to be actuated quickly and with a snap action, said spring being provided with notches for engaging said knife edges on said plate and said arms so that a pivotal connection is formed therebetween.

8. In a temperature control devicea rigid frame, a relatively thin, resilient, temperature responsive element secured at one end to said frame and having its opposite end free to move.,

said temperature` responsive element comprising a pair of reversely arranged bimetal sections. fixed contact means mounted on said frame. movable contact means associated with the free end of said temperature responsive element and adapted to be moved thereby to engage said fixed ycontact means to perform a controlling function,

resilient means for causing said temperature responsive element to move said movable contact means so that said controlling function is effected with a snap action, means for pivotally connecting said resilient means and said free end of said temperature responsive element, said pivotal connection between said resilient means and said free end of said bimetal element being spaced beyond the vertical line through the fixed and movable contacts when the latter are in engagement, and means for pivotally connecting said resilient member to a pair of fixed arms provided on said frame and lying intermediate the fixed and movable ends of said temperature responsive element so that said resilient means may exert a force on said element tending to stii'fen the same.

9. In a temperature control device, a frame, a relatively thin, resilient, temperature responsive element having one end secured to said frame and the opposite'end free to move, said element comprising two sections of bi-metal reversely arranged with respect to each other, control means associated with said temperature responsive element and adapted to be actuated thereby, resilient means for causing said temperature responsive element to be moved quickly and with a snap action, and an adjusting screw threadedly mounted in said frame and adapted to engage a surface of said temperature responsiveelement so as to affect the vertical component of the force exerted by said resilient means on the free end of said element so that the temperature setting of the control device can be altered between an off position for said control means at normal temperatures and a predetermined high temperature setting.

10. In a temperature control device, a support, a relatively thin compound bimetal blade element having one end secured to said support and the opposite end free to move, control means associated with said bimetallic element so as to perform a controlling function in accordance with movement thereof, resilient means for causing said element to be actuated.with afsnap action, means for pivotally securing said resilient means between a relatively movable pivot secured to the free end of said bimetallic elemen-t and a substantially rigid fixed pivot secured to said support so that said resilient means exerts a force on said bimetallic element tending to stiifen the same, and means adapted to bear against one surface of said bimetallic element for controlling the temperature at which said element is moved with a snap action tov alter the position of said control means.

11. A temperature responsive device comprising a compound bimetal element, a support to which one end of said element is fixed, xed contact means on said support, bridging contact means mounted on the free end of said element and adapted to engage said fixed contacts to perform a controlling function, resilient means pivotally secured to said support and said element to cause movement thereof to take place with a snap action, said resilient means exerting a vertical component of force on said free end of said blade so that a positive contact pressure exists between said fixed and bridging contacts, yand means bearing directly against a surface of said element for decreasing said contact pressure so that a lower temperature will cause said element to separate said contacts, said last mentioned means being movable to an extreme position to cause a force to be exerted on said element which completely overcomes said l a. snap action, said resilient means exerting a longitudinal force on said element tending to stiien said element and exerting a vertical force on the free end of said element so as to produce a. positive contact pressure between said contact members, and means bearing against a surface of said element for altering the eiect or said vertical component of force so that a di!- ferent contact pressure is produced between said contact members and a diilerent temperature is required to overcome said contact pressure so that said contact members are moved tothe open circuit position with a snap action, said last mentioned means being movable to a limiting position at which the force exerted on said element by said means is greater than the vertical component of force of said resilient means and said contact members are thereby manually moved to the open circuit position.

WALLACE J E'ITINGER.

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