US2611845A - Temperature control device - Google Patents

Description

Sept. 23, 1952 N. MILLER 2,611,845

TEMPERATURE CONTROL DEVICE Filed March :51, 1951 2 'flgms-sflmw 1 INVEIVTQR.

P 19.52 N. MILLER 2,611,845

TEMPERATURE CONTROL- DEY ICE Filed March 31, 1951 I SHEETS-SHEET 2 mm M JNVENTOR.

am 4M Patented Sept. 23, 1952 Nicholas Miller, Berwyn, Ill, assignor to Inc; a corporation of New York Hotpoint Application March 31, 1951, Serial No. 218,605

This invention relates to temperature control devices, and particularly to a thermostatic control having an improved switch contact actuating mechanism.

It is a principal object of the invention to provide a thermostatic control having an improved contact blade mounting and ing said blade between open and closed circuit positions.

It is another object of my invention to provide improved means for establishing an offpoint temperature setting at which the thermostat switch contacts will remain open even if the temperature-responsive elementsqwhich actuate the contact means are exposed to temperatures substantially below the, off-point temperature setting,

It is a further object of the invention to provide an improved operating relationship between a springable contact-carrying blade, a temperature-responsive actuating means for said blade, and a temperature-setting means.

A presently preferred embodiment of the invention includes a casing having a fixed switchcontact means mounted therein and a blade-like lever of flexible material pivotally housed within said casing and carrying a contact assembly :ior cooperation with said fixed contacts. An overthrow spring arranged betweenan adjustable pivot provided in a housing wall and a knife-edge 'end of said blade resiliently holds the blade in operating position and induces the blade to pass with a snap action between its open and closed contact positions, as is well understood.

A temperature-adjustment screw through a wall of the housing to bear on a surface of the contact blade to ex 'ert more or less pressure thereon according to the direction of rotation of the screw; and a thermosensitive system-for example, a liquidfilled system employing a flexible walled bellows connected by capillary tubing to a heat-sensitive bu1bis fixed within the casing at the opposite face of the blade, the axis of movement of said bellows being normal to the blade surface and midway between the screw axis and the blade pivot point. This is relatively conventional conextends struction; the blade pivot mounting and the adjustment screw provide spaced flexure points, and movement of the blade contacts relative to the casing contacts results from the action of the expanding bellows in bowing the blade between said points, with displacement of the contact end of the blade relative to the fixed contacts of the casing, When the bellows retracts on lowering means for operat-' and is arranged 8 Claims. (o1. sea-14o) iii ' tion will be apparent from temperature, the spring blade will assume a gradually increasing radius of curvature between the flexure points until its contact end returns through the overthrow point ofthe snapspring and assumes the opposite circuit position. Such thermostats have been used as amanually operated on-ofi switch for controlling a cook stove oven, for example, by merely turning the temperature-adjustment screw to a setting corresponding to a temperature below that to which the thermosensitive system would normally-[be subject. For example, it would be most unusu al for the temperature of the room in which the cook stove were located to drop below degrees F., and it would appear certain that at such a setting the thermostat would not operate to closed circuit position. However, it has happened that under certain winter time, conditions the thermo-- sensitive system may chill below this temperature and operate the thermostat switch. The circuit will almost immediately open, Qfcourse, because the oven heater will very quickly raise the temperature at the thermostatic bulb; but

assuming that the low room temperature may endure for a relatively long period-Jor' tor between thecontact blade and the'bellows' and provide a stop which will limit movement of the said actuator in a direction away from the blade. .In such arrangement the actuator supports the blade between the respective flexure points, and a rotation of the adjustment screw to an off position will flex the blade into open circuit condition, in which position it will remain regardless of any abnormal retraction of the bellows.

Other features and advantages of the invendescription of a presently preferred embodiment read in conjunction with the accompanying drawings, in which Fig. 1 is a side sectional elevation of a thermostat embodying my invention; Fig. 2 is a bottom plan view of the thermostat with the lower cover plate removed and the bellows system removed to show the, actuator means in greater detail; Fig. 3 is an end sectional elevation taken looking in the direction of the arrows 3-3 by other work-v the following detailed of Fig. 1; Fig. 4 is a view similar to Fig. 3 but showing the bellows in an exaggeratedly collapsed position to emphasize the operation of the actuator means; Fig. is a perspective of the pivot mounting block for the contact blade; and Fig. 6 is a front elevation of a, typical control dial showing the same in its off point position, as represented by Fig. 4.

The thermostat shown in cross. sectioninFigl is typical of those used for control of electric range ovens and the like. A casing l of any suitable insulation material provides an internal cavity of suflicient volume to hous the various operating elements.

with a screw-threaded aperture to receive the threaded shank 4 01: a spud having a shoulder 5 to which is brazed or otherwise tightly attached the open end of an expansible bellows 6 which may be of the conventional convoluted metal type.

The internal volume of the bellows may advantageously be reduced by projecting suitably into the bellows a body portion 1 of the spud. It will.

be obvious that the upper endof the spud limits the extent of retraction of bellows 6.. It is withe in the scope of the inventionto use a small volume chamber having a relatively large diameter fiexie ble top wall in place of the convoluted bellows;

A capillary tube 8 communicates between the bel= lows and a bulb (not shown) as is well understood inthe art; and as is also well understood, the bulb and tube system has a filling of liquid having predetermined vapor pressure and expansionichar acteristics to produce-a known amount of expane. sion and contraction of the bellows as'the bulb temperature increases or decreases over the. con; trol'range. The threaded'shank of the spud provides for. an adjustment of the Dositionof theibellows'within the casing; and a locknut or equiva lent 8 may advantageously be usedto secure the adjustment,

It;wi1l be assumedin the instant embodiment to indicate a restricted or specific application of The casing is enclosed by a suitable closure plate 2 in cooperation witha rela- T tively heavy base plate 3 which may be-provided blade 4 0 ,las later. appears.

with the rear-end portion of the blade. As shown in Fig. 2, the curving extension of the blade rearwardly of the forward faces of the stops 2| and 22 provides arcuate side portions which engage tangentially with the side walls of the stops 2| and 22 to secure the blade against appreciable side play within the block I l An adjustment screw 25 is mounted in a suitablewthreaded sleeve 2li fixed. within the casing wall, Thescrew'is normal to .one face of blade [0 and is threaded to provide a retraction of the screw when the same is rotated to increase the control temperature point. The round nose of screw- 25 provides a second fulcrum point for 7 As indicated in Fig. 6, the-calibration of the temperature setting knob 21 affixed to the screw calls for a clockwise rotation of the-knob to advance the temperature setting; The indicia of the knob are used with reference to the index mark 28 mounted on a suitable fixed escutcheon plate or the. like (not shown). In passing, it should be noted that the dial has an-off point which is representative of a temperature much lower than the lowest of the control range temperatures; for example, 150 degrees'F;

The blade-l0 has mounted at one end a carrier 30 -of-in'sulation'materiaL'which,in turn carries .50 and the. contact devices shown are not intended the thermostat. In either event, the contact v means or pilot valve, as the case maybe, .is near one. end ofa relatively stiflly flexible blade l0 sup: ported on, apivot block ll suitably'fixed within the casing; andinterposedbetween the. opposite end of theeblade and around-nose screw l2is a stiff, substantially U-sh-aped, snapspringj lf As is conventional, one leg of the spring may be dimpled at IE to provide a seat for the nose of screw l2,.and the opposite leg formed with a transverse-.

1y extending channel, IE to receive the knife-edge i The blade end is T-shaped 1 end; I! ofv blade. 10. to provide the mutually aligned edges I 8, 20 which are urged by spring l4 into engagement with the. faces 18a and 20a ofthe respective stops 2!, 22 of Between said stops the block is'formed block I l.

witha base portion.23 having a sharply defined edge 24. Said edge and the front faces of they stops are inaligmnent and all are normaltothe longitudinalaxis of the blade l0.= Edge--24 provides a pivot point for blade 10, as later described;

it will be noted in Figs. 1 and 5 that base. 23 slopes downwardly to the rear to avoidconfiict contact plates 3| respectively cooperating with pairs of fixed contacts, such as the contacts 32, carried by the casing and arranged by any suitable means: (noti'showm' "for connection into an electrical circuit to bejcontrolled. The use of two contact plates'and two pairs .of fixed contacts provides fora double-pole, single-throw, switch circuit. Thecontztctcarrier hasa pairof stops 33 symmetrical with'respect to the rivet or the like 34 with which the. carrier is rockably fixed to theblade: [0. Said. stops cooperate with a pairof stop-screws '35Scarried by a tongue 36 struck'upwar-dly'from:plate 3. The contact carrier and contact plate arrangement are common in the artand fo'rmxno part of the present invention;

The movement 'of thebladeifi to establish a particular circuit. position. of. the contact carrier results from'the flexing of the blade between the flexure'points' provided by the fulcrum edge 24 of block I I and the nose of screw 25. Such flexure'is derived ibythemoyement of the bellows 6 with respect: totblade .IOJ. More particularly, in the present llIlVGIltlOIlI .interpose between the head 31 of the bellows and the blade l0 an actuatoryfor example, a rigid, lever 38 hinged at one end to a bracket 3.9"secured appropriately to the housing I. Said actuator most preferably has a rivet or button). at. the longitudinal centerline of blade H1. The buttonprovides a flat top 4| for cooperation with'adimple 42 formed in blade I0 and a domed'bottom 43 having a point contact withthe center of.head 31. of the bellows 6. Movement of the bellows .upwardly of Fig. l is transmitted to blade 1 0' 'atsubstantially the longitudinal axis thereof. Acstopscrew or-support 44 mounted in base...plate -.3v for ready adjustment;

supports thefend of the. actuator 38 in such position that even under. abnormally low temperature conditionsinwhichthe head-of the bellows may disengage from.the. aotuator, the blade ill will.

snap spring M is in its upper overthrow position. The closed circuit position of the contacts will remain until the expansion of the liquid filling of the thermosensitive system expands the bellows 6 with sufficient force" against actuator 38 to cause the actuator to bow the blade upwardly between the respective flexure points and correspondingly enforce a downward deflection of the contact end of the blade. When edge ll of blade l passes through the overthrow point of spring M, the latter overthrows downwardly to break the contact engagement with a moderate snap action. In open contact position the stop members 33 of the contact plate mounting rest upon the stop screws 35. controlled space falls, the reduction of pressure within the tube system permits the bellows to collapse. The spring blade assumes a lessening curvature as it relaxes from the enforced distortion until its contact end rises through the overthrow point of spring It and the contacts return to closed position. i

It has been observed that the actuator 38 is positioned by stop screw M so as always to maintain blade l8 on fulcrum it regardless of the extent of retraction of bellows 6. This function of the actuator not only makes it possible to eliminate friction-producing pivot constructions which would positively hold the end of blade ii? on the pivot block, but also adapts the thermostat for operation as an on-olf switch which will be effective even though the bellows may collapse to the stage of actual disengagement from the stud d0. V

It should be understood that the adjustment of screw M is such that actuator 3!? always exerts abias on blade H3 suificient to throw the blade from an open to a closed-circuit position if the knob is rotated to a high temperature setting under an abnormal temperature condition in which bellows 6 is not exerting any upward effort on the actuator. With this in mind, it will be noted that when the knob 2'! is rotated counterclockwise of Fig. 6 until suitable stop means, such as an appropriate pin and shoulder arrangement 85, i6, positions the off marking of dial 2? at the index 28, the screw 25 willbe projected downwardly to enforce a sharp downward defiection of blade is to the right of actuator 38, as viewed in Fig. i. In such position the con tacts will be in open-circuit disposition. If at the time the bellows were expanded, as might be the circumstance immediately after baking, the blade may have a convex curvature intermediate fulcrum 2 3 and screw 25, and a concave curvature between the screw and the stops 35. As the lowering temperature of the thermosystem produces a contraction of bellows 6, the fiexure of the blade to the left of screw 2 s"-(as viewed in Fig. l) diminishes until at the engagement of As the temperature of the lever-type actuator is that it provides for relatively fine adjustment of the contact blade with a relatively coarse threaded adjustment screw. The lever arrangement also provides a convenient means of positioning the actuator coaxial with the bellows and therefore maintaining the symmetryof the system. For example, to arrange a stop screw to bear directly against blade Ill in lieu of the actuator'38, would require in order to clear the bellows that :the screw be placed closer to the adjustment screw 25 or to the fulcrum 24. In either case, this would result in an unbalanced fieiiure pattern of the blade [0, with possibly damaging results.

While there has been described what is at present considered to. be the preferred embodiment'ofthe invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such'modifications as fall within the true spirit and scope of the invention.

I claim 1.;In a thermostat, a casing, a pivotv block therein, said pivot block having a base portion, mutually spaced wallstru'ctures extending there- I from, said base portion having a sharply defined actuator 38 with stop M blade it assumes a comparatively simple downward fiexure from the actuator to the stops 35. The reaction of blade l 0 at the left of actuator 38, holds the thermostat in oil position so long as the setting knob is maintained in that position. Despite the movements of bellows 6, the contacts will remain open. To close the circuit, knob 2i need merely be rotated to retract screw 25, and because of the biasing effect of actuator 38, as above noted, the blade will follow into closed circuit position. Thus, the on and off positions of the thermostat may be attained as desired'regardless of the relation between the bellows 5 and the contact blade.

It will be obvious that an advantage of the ridge extending between said wall structures in alignment with common end surfaces thereof, a flat, flexible, blade-like'member supported at one end on said ridge and having sidewardly extending portions engaging said end surfaces, means for resiliently urging said blade portions into engagement with said surfaces, contact means carried at the'opposite end ofsaid-blade, cooperating contact means carried by said casing, an adjustment screw extending into said'casing and engageable with a' surface of said blade to exert pressure thereon in a direction tending urging the blade away from said pivot block base, a tem-- perature-sensitive system including a member disposed in said casing at the opposite side of said blade and having wall means movable toward or away from said blade according to the change in temperature of said system, actuator means interposed between said blade and said "movable wall means intermediate said adjustinent screw andsaid pivot block, means mounting said actuator means for movement in the directions of movementof saidwall means, and means'for limiting movement of said actuator away from said blade toan ultimate position at which said actuator maintains the said blade on said pivot block edge regardless of extreme withdrawal of said wall means relative to said blade, whereby said adjustment screw may be'used under any temperature condition to flex the blade about said actuator means for establishing a de sired relationship between the blade contacts and the casing contacts.

2. In athermostat, a casing, a pivot block therein, said pivot block having a base portion, mutually spaced wall structures extending therefrom, means on said base portion providing a sharply defined fulcrum extending between said wall structures, said fulcrum and common end surfaces of said wall means being in alignment, a fiat, flexible, blade-like member supported at one end'on said fulcrum and having sidewardly extending portions engaging said end surfaces, overthrow spring means interposed between said casing and the opposite endcf said bladelike member for resiliently urging said blade portions into engagement with said surfaces, contact means carried at said opposite end of said blade, cooperating contact means carried by said casing, an adjustment screw extending into said casing and engageablewith'asurface of said blade, said screwbeing operativ when rotated in one direction to urge the bladeaway from saidpivot block baseand to separate the respective blade and casing contacts, a temperature-sensitive system including a, member disposed in said casing at the oppositev side of said blade intermediate said. adjustment screw and said pivot block and having wall means movable toward or away from said blade according to the change intemperature of saidsystem, an actuator lever pivotally mounted in said casing and extending transversely across said blade between said blade and said movable 'wall means, and adjustment screw means for. supporting said actuator lever from separationfrom said blade, said screw causing said blade tobear on said fulcrum and flexing said blade to maintain the respective contacts in a predetermined circuit condition despite the retraction of both said first-named adjustment screw and said temperature system wall means away from said blade.

3. In a thermostat, a casing, a pivot block therein, said pivot block having a base portion, mutually spaced wall structures extending therefrom, said base portion having means providing a sharply defined fulcrum extending between said wall structures, said fulcrum and common end surfaces of said wall means being in alignment, a flat, flexible blade-like member supported at one end on said fulcrum and having sidewardly extending portions engaging said end surfaces, means'for resiliently urging said blade portions into engagement with said surfaces, contact means carried at the opposite end of said blade, cooperating contact means carried by said casing, an adjustment screw extending into said casing and engageable with a surface of said blade to urge said blade away from said pivot block, a temperature-sensitive system including a member disposed in said casing at-the opposite side of said blade intermediate said adjustment screw and said pivot block and having wall means movable toward or away from said blade according to the change in temperature of said system, an actuator lever pivotally mounted in said casing and extending transversely across said blade between said blade and said movable wall means, and adjustment screw means engaging said actuator lever to cause said lever always to maintain said blade on said pivot block fulcrum regardless of the temperature of said temperature-sensitive system and the position of said wall means resulting therefrom.

4. In a thermostat, a casing, a flexible blade member pivotally mounted at one end within said casing, contact means carried by said blade member near its opposite end, cooperating contact means carried by said casing, an adjustment screw extendinginto said casing and engageable with a face of said blade member to displace the contact end portion thereof relative to said cooperating contact means, an actuator lever pivotally mounted within said casing and extending transversely across the opposite face of said blade member intermediate the fulcrum point thereof and the point of engagement of said adjusting screw With said blade member, stop means engaging said actuator lever and maintaining the same in engagement with said blade member'while supporting said lever for. operation as a fulcrum about which said blade member may flex upon operation of said adjustment screw to exert pressure thereon, and a temperature-sensitive system-including a member disposed within said casing and having wall means arranged upon predetermined change in temperature to .engage said actuator lever to 1'0- tate the same in the direction of said blade member to flex said member over the expanse thereof intermediate its fulcrum point and the point of engagement of said adjustment screw.

5. In a thermostat having a casing, a fiat, elongated, flexible blade therein, fulcrum means in said casing extending across one face of said blade at one end thereof, contact means carried by said blade near the opposite end thereof-for cooperation with fixedcontact means carried by said casing, and a screw member mounted in said casing for movement normal to said blade face and engageable therewith intermediate the ends thereof to establish a second fulcrum point; means for flexing said blade to actuate the free end thereof between open and closed circuit positions, comprising a thermoresponsive system including an element fixed at one end to said casing and having a wall portion disposed adjacent the opposite face .of said blade, said wall portion being movable toward or away from said blade according to the change in temperature of said system, said movement being in a direction substantially in the direction of flexure of said blade, actuator means disposed between said fulcra and interposed between said wall portion and said blade, said actuator means being in engagement with said wall portion and said blade over a predetermined operating range of temperature of said thermosensitive system, means for mounting said actuator means for movement in the direction of blade flexure, whereby movement of said wall portion toward said blade will cause said actuator to exert a flexing action on said blade intermediate said fulcra to displace the contact end of said blade relative to said fixed contacts, and means engaging with said actuator means at a predetermined position of said thermoresponsive element wall means to position said actuator means for continued support of said blade in engagement with said first fulcrum in the circumstance of separation of said wall means from said actuator means resulting from the exposure of said thermosensitive system to a temperature outside of said normal operating range.

6. In a thermostat, a casing, a pivot block therein, a flat, flexible, blade member pivotally seated at one end on said pivot block, contact means carried by said blade at the opposite end thereof, cooperating contact means carried by said casing, a manually operable adjustment screw extending into said casing and engageable with a face of said blade, said screw being eifective when rotated in one direction to urge said blade toward separation of the respective contact means, a temperature-sensitive system having a predetermined operating temperature range, said system including a member fixed within said casing adjacent the opposite face of said blade and having wall means eflective to exert or relax pressure on said blade according to the change in temperature of said system, the locus of said effort being intermediate said pivot block and said adjustment screw, and means engaging with said opposite face of said blade to maintain said blade seated on said pivot block, said blade-engaging means being disposed intermediate said adjustment screw and said pivot block and biasing said blade to closed circuit position while affording a fixed point about which said blade maybe flexed into a permanently open circuit position when said adjustment screw is rotated in said one direction to a predetermined degree.

7. In a thermostat, a casing, a pivot block therein, a fiat, flexible, blade member pivotally seated at one end on said pivot block, contact means carried by said blade at the opposite end thereof, cooperating contact means carried by said casing, a manually operable adjustment screw extending into said casing and engageable with a face of said blade, said screw being effective when ro-' tated in one direction to urge said blade toward separation of the respective contact means, a temperature-sensitive system having a predetermined operating temperature range, said system including a member fixed within said casing ad- Jacent the opposite face of said blade and having wall means efiective to exert or relax pressure on said blade face according to the change in temperature of said system,the locus of said pressure being intermediate said pivot block and said ad- Justment screw, and a lever pivotally mounted relative to said blade and engaging with said opposite face of said blade to maintain said blade seated on said pivot block under circumstances in which said adjustment screw and said wall means may each be retracted from said blade, said blade-engaging lever being disposedintermediate said adjustment screw and said pivot block and adjusting screw means for urging said lever against said blade for biasing said blade in a direction effective to bring the respective contacts into closed circuit position upon retraction of the first-named adjustment screw from said blade.

8. A thermostat comprising, in combination, a casing, a lever having a flat end portion formed with wings extending laterally from opposite sides thereof, said wings having rear edges in mutual alignment and normal to the longitudinal axis of said lever, the portion of said lever intermediate said wings extending rearwardly thereof, pivot means fixed within said casing, said means including mutually spaced rigid side walls having upwardly extending common wall portions in mutual alignment to provide abutments engageable by the said rear edges of said wings, wall means intermediate said side walls providing a fiat, sharply defined, ridge operable as a fulcrum for said lever portion intermediate said wings, said ridge being in alignment with said common wall portions and in a plane intermediate the ends thereof, means within said casing remote from said pivot means for maintaining said lever portion on said ridge, overthrow spring means interposed between the opposite end of said lever and said casing for maintaining said wings resiliently against said side wall portions, a thermosensitive system associated with said lever for rotating the same about said ridge responsive to temperature changes of said system, and means for utilizing said lever movement to control a heat source.

NICHOLAS MILLER.

REFERENCES CITED UNITED STATES PATENTS Name Date Hook Dec. 11, 1928 Number

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