US2255169A - Thermal relay - Google Patents

Description

p 9, 1941- M. IRELAND 2,255,169

THERMAL RELAY Filed June 21, 1939 35 Inventor:- Murrou Ireland KttSFT-Zg.

Patented Sept. 9, 1941 THERMAL RELAY Murray Ireland, near Elgin, 11]., assignor to McGraw Electric Company, Chicago, 111., a corporation of Delaware Application June 21, 1939, Serial No. 280,284

13 Claims.

My invention relates to thermal control devices and particularly to snap-acting bimetal thermostats.

One of the objects of my invention is to provide a novel snap-acting bimetal thermostat having a relatively small temperature differential of operation.

Another object of my invention is to provide a snap-acting thermally responsive device including at least one compensating portion.

Other objects of my invention will either be apparent from a description of a preferred form of my device or will be set forth in detail in the course of the description thereof.

In the single sheet of drawings,

Figure 1 is a longitudinal vertical sectional view, of a thermal relay embodying my invention, taken on the line L-l of Fig. 2, showing the bimetal bar in one limiting position,

Fig. 2 is a top plan view thereof,

Fig. 3 is a side elevational View showing the bimetal bar in the opposite limiting position,

Fig. 4 is a vertical sectional view taken on the line L4 of Fig. 3,

Fig. 5 is a horizontal sectional view taken on the line 55 of Fig. 3,

Fig. 6 is a top plan view of a modified form of bimetal bar,

Fig. '1 is a plan view showing another form of bimetal bar,

Fig. 8 is a cross sectional view taken on the line 8-8 of Fig. '7,

Fig. 9 is a side elevational view of a bimetal bar with a heating coil around the end opposite from that shown in Figs. 1, 2 and 3, and

Fig. 10 is'a fragmentary detail view showing a modified form of bimetal bar and its mountin .v

' will be the temperature change required to cause the bowed strip to snap across its fixed axis of pressure.

It is sometimes desirable to reduce this change of temperature necessary to cause a change of shape of the initially bowed bimetal strip while still causing a change of shape to occur with relatively large power or with relatively vigorous movement thereof and this may be done by adustable stops engaging the ends of the bowed strip.

Referring first to Figs. 1 and 2 of the drawing, I have there illustrated a frame H which may be made of some electric-insulating material, of substantially L-shape, that includes a main part 13 and a lateral extension 15 thereon, which lateral extension is provided with a lateral notch or recess 11 in its inner face, which recess is of substantially V-shape in section. At the other end of the main part 13 there is mounted a resilient bearing member I! which may be of metal and of substantially L-shape. As shown in Fig. l of the drawing, a lateral portion 20 of member I 9 may be secured against the bottom face of part I: by one or more screws Zl'while the main part may be adjusted relatively to the part 15, that is, toward and away from portion 15, by an adjusting screw 23, the initial shape of member I! being such that it is hent away irom the part I! of the support it. in order to prevent turning movement at member H on the end of part 13, a pair of spaced extensions 25 may be provided between which the main part of member l9 extends upwardly as shown in Figs. 2 and 5 of the drawing.

A flexible bimetal strip 21, which may be of the form shown in Fig. 2 of the drawing, is mounted in the frame II. Bimetal element 21 is preferably but not necessarily constructed from an initially integral strip having the width shown at the right-hand portion of the form shown in Fig. 2, while anL-shaped slot 39 is provided which divides the strip, 21 into two parts. One of these parts is the main portion or leg 3| of full width for a relatively large part of the length of the strip and then a narrower or auxiliary or .compensating portion 33 which is narrower than the portion 3|. The right-hand end of element 21 is preferably beveled as shown at 35, Fig. 1, and an aperture 31 is provided in the free or inner end of portion 33.

The beveled end 35 of the main portion 3| fits into the recess 11, of V-shape, in portion l5 of the supporting frame and the upper end of member 19 extends into and through the aperture 31, there being a knife-edge bearing between member I! and a wall of the aperture 31. The upper end of member I! is made narrower than the other part thereof, 'to fit into aperture 31.

I provide apair of adjustable stop members on the frame ll, each of which is preferably of metal and include a relatively long shaped bar I! and-a shorter shaped bar 4|, the lower ends tions 3| and in which the main bowed portion tends to move and will finally move, after a predetermined of each of which are secured to the portion l3 by a plurality of short machine screws 43. Each of these stop members includes an adjustable contact member in the shape of short machine screws numbered respectively 45 and 41. While I have specified that members 45 and 41 are contact members, this is the case only if the device justable machine screws. A small electric heater 49 may be supported as by being mounted on the frame II in any suitable or desired manner. I have shown this coil as being substantially selfsupporting and as being wound around a part only of portion 3| of the main part of the flexible strip. I do not desire, however, to be limited to this position of the auxiliary heating element, the energization of which may be controlled by the movements of the flexible bimetal strip, since this heater may be located in other positions relatively to the thermally responsive strip as will be hereinafter referred to in greater detail.

It will be noted that flexible bimetal strip 21 is unitary and comprises two side-by-side portions, combined to make a member of substantially u-shape, the main and auxiliary or compensating portions being normally coplanar. When the flexible bimetal strip 21 has been mounted in its proper operative position in the two bearings in members l5 and Is, as hereinbefore described, the adjusting screw 23 may be so turned that the flexible support I9 is moved in a clockwise direction (as seen in Fig. 1 of the drawing) whereby a tension stress is placed upon auxiliary portion 33 and acompression stress is placed on the main portion 3|. This will result in the portion 3| assuming an arcuate or bowed shape. The less the distance between the two points of the discrete support II, the greater will be the bowing of the main portion, provided, of course, that the strip is permitted to bow freely. It will be noted that the distance between the supporting points on the discrete support is less than the over-all length of the strip and that the device embodying my invention provides two pivotal bearing supports, one of which is in abutting relation with the bimetal strip and the other of which is in interfitting relation therewith. The axis of pressure of the main portion 3| extends from the bearing in notch 11 to the connection between the adjacent ends of the portions 3| and 33 at the left hand end of element 21, as seen in Fig. 1.

It is, of course, obvious that the greater the amount of bowing of the main portion 3|, the greater will be the change in temperature required to .cause it to snap across its axis of pres-- sure and that the greater thebowing the greater will be the temperature difierential of operation of a device of this kind. However, it may be further pointed out that the compensating portion 33 is efiective to reduce this temperature difierential of operation because of its action in moving the point of connection of the two por- 33 in a direction opposite to that change of temperature. This is because the high temperature component in the ,flexible bimetal strip is on the same side of both portions. Fig. 3

shows the shape of the flexible strip after it has been subjected to a predetermined change of temperature suficient to caiise it to move over into an oppositely bowed shape. 4

As stated abovethe greater the bowing or the main portion 3|, the greater the change of temperature necessary to cause it to move from its initial bowed position to an oppositely bowed position. The auxiliary portion 33 compensates for the eflect of this bowing of portion 3| on its operation by reducing the amount of bowing of the main portion 3|, since it causes lateral movement of the point of connection of the two portions in a direction opposite to that in which the mid portion of part 3| tends to move in response to temperature changes. It is thus possible to obtain efiective snap action of the main portion 3| from one position to another position with relatively small temperature changes acting on the thermostat.

Itwill be noted further that the axis of pressure is not stationary as in all of the earlier'devices of this general kind with which I am fa miliar, but that it is movable and tilts around the end 35 of the main bimetal portion and that it moves in a direction opposite to the direction of movement of the main portion of the flexible strip 21'.

Referring now to Fig. 6, I have there shown a modified form 5|' of the main bimetal strip in which a part of the main portion 53 is slightly wider than the adjacent auxiliary or compensating portion 55. This latter portion is longer than the portion 33 of bimetal strip 21. The' thermal lag of part 53 will be much greater than the thermal lag of portion 55, hence the compensating action will be relatively large The'greater the length of a bimetal strip, thg greater is its response to any given change of temperature, and the auxiliary portion 55 would therefore be more active than would be-the case with the auxiliary portion 33 of bimetal strip 21 of Figs. 1 to 5.

Referring now to Figs. 7 and 8 of the drawing, I have there shown a built-up thermal element 51 comprising a relatively heavy and long main bimetal portion 59 and an auxiliary or compensating portion 6| shorter than the main portion and also thinner. These two strips have an end of each in side-by-side adjacent positions, which ends are connected by a cross bar 53 and rivets or other suitable securing or holding means. In allother respects this element 51 operates in exactly the same manner as was hereinbefore set forth for bimetal element 21. The main portion 59 being relatively heavy will respond to any change of temperature more slowly than will a thinner or narrower strip such as is shown for as in portion 55, relative to the main portion.

11:, on the other hand, a device having but small thermal mass is to be controlled by a thermally responsive device of the kind shown in the drawing, the main portion can. be made to have relatively small mass, as by using a thin main portion, and where for any reasonv relatively sluggish compensation is desired, the co'mpensat other modifications already referred to. The end portion 13 thus overhangs the support is and may be used to control and actuate electrical or mechanical devices not shown.

I may also use a single main bar ll and two auxiliary compensating bars 33 to form a thermostat of flattened c-shape, in which case the construction of Fig. would be used, the support 65 then engaging the second compensating bar instead of the main bar, the thermal relay then having an increasedsensitivity and a reduced temperature differential orv operation.

I have found it possible also to vary the come pensating action by the location of the auxiliary heating element 49 which can be connected in series circuit with the thermal relay to have its energization controlled thereby in a manner well .known in the art. Thus when the heating element II is positioned near that end of the flexiblebimetal strip remote from the connected end of the compensating strip, as shown in Figs. 1, 2 and 3, the compensating strip will be heated mainly-by heat conducted from the far end of the main portion through the length of the main portion and from there across the bridge connecting the end of the main portion with the adjacent end of the compensating portion. Thus if a device of this kind be used as a thermal timer to control a plurality of closely succeeding repetitive cycles of operation, as in automatic toasters, it may be desirable or necessary to provide definite degrees of compression of the main portion or compensating effect of the auxiliary portionto adapt the thermal relay to the time temperature curve of the diiferent devices with which it maybe associated.

As an example of definite positions of the heating element 49, it may be moved farther toward the compensating portion of the bimetal strip or it may even be located around the left-hand end of strip 21, as shown in Fig. 9, in which case heat radiated therefrom will affect not only the main portion but also simultaneously the auxiliary portion 33, whereby an early compensating effect may be obtained in the operation of the thermal device.

This latter construction, that is the one where the auxiliary and the narrow part of the main portion of the bimetal strip are simultaneously subjected to change of temperature, will be of value in thosecases where it is desired to obtain a relatively small temperature differential of operation of a thermal relay of the kind herein disclosed.

It is obvious that my improved thermostat can also be operated by a reduction in temperature instead of an increase in temperature and that the use of an auxiliary heating means or of an auxiliary cooling means is optional and that the thermostat may be made to operate to control heat or cold by being subjected solely to the temperature of the ambient air or of a mass or member, the temperature of which is to be controlled.

not desire to be limited thereto as further modifications may be made and all such modifications coming within the scope of the appended claims are to be considered as part of my invention.

I claim as my invention:

1. Asnap-acting bimetal thermostat comprising a main part having a predetermined length and a shorter compensating part having one end secured to one end of said main part and extending toward the other end of the main part and discrete supporting means engaging the other end portions of said main and compensating parts and applying stresses of. different character thereto which result in a bowed shape of the main part.

2. A snap-acting bimetal thermostat comprising a relatively long main part and an integral shorter compensating part normally coplanar with each other and of substantially U -shape and supporting means having a length less than that of the main part and engaging the free ends of the main and the compensating parts to apply compression to the main part and tension to the compensating part, said compressive stress causing a bowing of the main part to one side of the axis of pressure of the main part, change of temperature causing a quick movement of the main part across said axis of pressure.

3. A snap-acting bimetal thermostat comprising unitary main and auxiliary portions normally coplanar and partially coextensive with each other and supporting means having one part thereof in interfltting relationship with one of said portions and causing abutting relationship of the other portion with another part of the support, the distance between the 'two parts of the supporting means beingless than the length of the main portion by substantially the length of the-auxiliary portion.

4. A snap-acting thermo-responsive device comprising a flexible strip of bimetallic material divided into two connected parts by an L-shaped slot therein and bearings pressing oppositely on the respective parts, at least one of said bearings being pivotal, acting to initially how one of said parts; a change of temperature causing said bowed part to move across the axis of pressure into an oppositely bowed position.

5. A snap-acting thermo-responsive controlling device comprising a flexible strip of bimetallic material divided into two connected parts by an L-shaped slot therein and a pair of spaced supports respectively pivotally engaging an end portion of the parts of said strip to initially compressively stress and bow one part of said strip and to tension the other part of the strip.

6. A theme-responsive device comprising a pair of pressure-exerting bearings and a flexible strip of bimetallic material having an L-shaped slot therein to divide the strip into two partially coextensive connected parts, the free ends of the parts of said strip being pivotally supported by said bearings whereby one of said parts is stressed in tension and the other of said parts is stressed in compression and initially bowed'and parts of the strip, the strip being so mounted that the supporting means exerts a tension stress on one of said parts and a compression stress on the other of said parts causing it to bow and to snap from one bowed position to an oppositely bowed position across a movable axis of pressure in response to changes of temperature, said axis of pressure tilting in a direction opposite to that of the movement of the snap-acting part.

8. A snap-acting bimetal thermostat compris-' ing a main and a shorter auxiliary portion normally in coplanar positions with adjacent ends secured together and discrete supporting means having two thermostat-supporting bearings pivotally engaging the respective portions at points spaced a shorter distance apart than the length of the main portion with the connected ends of the two portions positioned at one side of the axis of pressure .of the supporting means, said supporting means applying an adjustable compressive stress to the main portion to cause it to assume an arcuate shape at one side of a floating axis of pressure and move to the other side of said axis of pressure with a quick action on being subjected to a predetermined change of temperature.

9. A snap-acting thermally responsive device comprising a flexible main bimetal bar and means for supporting it in initially bowed posi: tion including a flexible auxiliary bimetal bar integral with the main bar at one end and partially coextensive therewith and two pivotal bearings engaging respectively the free end portion of the main bar and the free end portion of the auxiliary bar to subject the main bar to an initial longitudinal compression stress, said main bar being thereby bowed and moving across the axis of pressure with a snap-actionon change of temperature, said axis 'of pressure tilting in an opposite lateral direction relatively to the direction of movement of the main bar around the point of engagement of the main bar witli' its bearing. I

10. A snap-acting thermosensitive device comprising a flexible bimetal member of substantially U-shape having normally coplanar legs of unequal length and means including the shorter leg for supporting the longer leg at two spaced points in initially longitudinally compressed-condition to cause it to assume a bowed shape, change of temperature causing said longer: leg to move across an axis of pressure passing through said two supporting points, which axis of pressure turns in a direction opposite to that "of the movement of said long'er leg.

, 11. A snap-acting theme-responsive device comprising a flexible bimetal'strip having a main part and at least one compensating part normal- 1y coplanar with each other in flat side-by-side and partially coextensive positions and discrete supporting means engaging the strip at two points a lesser distance apart than the length of the-main part, said supporting means applying an adjustable compressive stress to the main part to cause'it to assume an arcuate shape at one side of a floating ZJfiS of pressure passing through the two points of support and to move across said axis of pressure with a sudden action on being subjected to a predetermined change of temperature.

12. A snap-acting thermo-responsive device comprising a flexible bimetal strip including a -main part and at least one compensating part normally coplanar with each other in flat sideby-side and partially coextensivevpositions and an adjustable support for the strip engaging the same at two points spaced apart a distance less than the length of the main portion, said supporting means applying a tension stress to the compensating part and a compressive stress to the main part to cause the main part to assume a bowed shape at one side of an axis of pressure passing through the two points of support and to move across said axis of pressure with a quick action on predetermined change of temperature, said axis of pressure'moving laterally in a.direction opposite to the direction of movement of the main part and simultaneously therewith.

13. .A snap-acting thermo-responsive device comprising a flexible metal strip having a main part arid two compensating parts, the respective outer ends of the compensating parts being connected to the ends of the main part to cause the compensating parts to be partially coextensive with the main part and to have their inner ends extend toward each other at one side of and normally coplanar with the main part and discrete supporting means engaging the inner end portions of the compensating parts to apply tension stresses to the compensating parts and a comsnap action on predetermined change of temperature, said axis of pressure moving laterally simultaneously in a direction opposite to the direction of movement of the main part.

MURRAY IRELAND.

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