US2851971A - Thermo-responsive control - Google Patents

Description

Sept. 16, 1958 Filed Aug. 26, 1953 D. T. CAMPBELL 2 Sheets-Sheet 1 Room mERIAOSTAT' l W 23:31 I 20 I I27 79% a2 46 16 I A" I I A 60/ I LmE 76 v 46 GT I 10 a? INVENTOR. .DAVJDZ CZIYPEELL ATTOII'NEZ Sept? 1958 D. T. CAMPBELL 2,851,971

THERMO-RESPONSIVE CONTROL.

Filed Aug. 26, 1953 2 Sheets-Sheet 2 IIIWI HIIII H lllllilllllll IN V EN TOR. 0.41/10 7. CQJIPEELL;

United States atent TWO-RESPONSIVE CONTROL David '1. Campbell, Indianapolis, Ind.

Application August 26, 1953, Serial No. 376,641

3 Claims. (Cl. 110-1) The present invention relates to a thermofresponsive control, and is concerned primarily with the provision of a control of the character indicated, specially useful in a system for controlling the ignition and operation of a solid fuel, Stoker-fed, burner. Basically, I have provided a thermo-responsive unit including a bimetal bar, or its equivalent, which, under conditions of use, is initially movable under the influence of heat transmitted thereto by conduction, and which is subsequently movable, in the same direction, under the influence of heat transmitted thereto by convection.

It is a primary object of the invention, then, to provide a thermo-responsive control including a bimetal bar, or its equivalent, a portion of which rests, under relatively low temperature conditions, in contact with an element having a relatively high coefiicient of heat conduction, the bar being so supported that, upon an increase in its temperature, the said portion of the bar will move away from, and out of contact with, the highly conductive element; and in which said bar portion, upon further increase in temperature, will continue to move farther and farther from said element of high heat conductivity. A further object of the invention is to provide a system in which the movable portion of such a bimetallic bar will, upon initial movement under the influence of heat transmitted thereto by conduction, shift a controlled element; and, upon further movement in the same direction under the influence of heat transmitted thereto by convection, will shift another controlled element.

A still further object of the invention is to provide, in a system of the character suggested above, an arrangement whereby the shifting of the first controlled element will deenergize an ignition device, while the shifting of the second controlled element will throw the entire system out of operation.

Further objects of the invention will appear as the description proceeds.

To the accomplishment of the above and related objects, my invention may be embodied in the form illustrated in the accompanying drawings, attention being called to the fact, however, that the drawings are illustrative only, and that change may be made in the specific constructions illustrated and described, so long as the scope of the appended claims is not violated.

Fig. 1 is a diagrammatic illustration of a solid fuel burner, ignition and stoker means therefor, and a control system for such ignition and stoker means, embodying my invention;

Fig. 2 is a sectional view, drawn to an enlarged scale, and showing the thermo-responsive control which constitutes a feature of my invention; and

Fig. 3 is an end elevation of the unit of Fig. 2, viewed from the left.

In Fig. 1, I have diagrammatically illustrated a solid fuel burner such as a household furnace, indicated by the reference numeral and formed to provide a combustion chamber 11. A stoker mechanism, indicated genice erally by the reference numeral 12, is suggested diagrammatically and includes a driving motor 13. Within the combustion chamber, I have indicated an electric ignition unit 14, but it will be understood that any kind of ignition unit may be used in the present system, so long as it is capable of being activated electrically.

At 15, I have indicated the conventional smoke pipe or stack, leading to a chimney 16; and at 17, I have indicated a conventional room thermostat. The illustrated system is a high voltage system, using household circuits; but it will be clear that my invention is applicable, also, to systems in which the control circuits are secondary, low-voltage circuits.

The two sides of a household current supply are indicated at 18 and 19. The line 18 is connected to the stationary contact 21) of the room thermostat 17, while a movable contact 21 thereof is conventionally supported upon a bimetallic, thermo-responsive bar 22. A wire 23 connects said contact 21 with one contact 24 of a limit switch, indicated generally by the reference numeral 25. The other contact 26 of the switch is connected by a wire 27 with the movable element 28 of a double-contact switch indicated generally by the reference numeral 29. The switch 29 is so constructed and arranged that, under normal conditions, the contact 28 engages a contact 30 thereof, said contact 23 being movable, under conditions later to be described, out of engagement with the contact 30 and into engagement with the contact 31.

A wire 32 leads from the contact 28 of the switch 29 to a movable contact 33 of a switch indicated generally by the reference numeral 34. The stationary contact 35 of the switch 34 is connected, by wire 36, with one terminal of a motor 37, the other terminal of which is connected by wire 38, with the line wire 19.

A wire 39 connects wire 32 with the movable contact 40 of a further switch 41, the stationary contact 42 of which is connected, by wire 43 and a wire 44, with one terminal of the motor 13, the other terminal of which is connected to line wire 19. A wire 45 connects wires 43 and 44 with the contact 31 of switch 29.

A wire 46 leads from contact 31 of switch 29 to the wire as; and a wire 47 connects said wire 4-6 with the stationary contact 48 of a further switch 49, the movable contact 54) of which is connected, by wire 51, with one end of the igniter unit 14, the other end of said unit being connected, by wire 52, with line wire 19.

Motor 37 drives a triple cam wheel comprising cam surfaces 53, $4 and 55. The movable contact 33 of the switch 34 carries a finger 56 which rides the cam surface 53; the movable contact 4t) of switch 41 carries a finger 57 which rides the cam surface 534; and the movable contact 5d of the switch 49 carries a finger 58 which rides the cam surface 55.

Fig. 1 illustrates the rest positions of the parts of the control system. When the room thermostat 17 calls for heat, a circuit energizing the motor 37 is established from line wire 18 through thermostat contact 2 contact 21, wire 23, contact 2% of switch 25, contact 26, wire 27, contact 28, contact 31 wire 46, wire 36, motor 37, wire 38, and line wire 19. The motor 3'7 is thus energized to drive the cam wheel in a clockwise direction. The system is so proportioned and designed that the motor 37 will drive the cam wheel through one revolution in twenty minutes. During the first minute of such operation, the finger 56 rides the node of the cam surface 53, the finger 58 rides the node of the cam surface 55, and the finger 57 rides the node of the cam surface 54, so that all of the switches remain in their illustrated conditions. If, during this period, the contact 28 of the switch 29 should be moved out of engagement with the contact 31), or if the contact 26 of the switch 25 should be moved out of 3 engagement with the contact 24, the motor 37 will be stopped.

However, if the elements of the control unit 59 remain in their illustrated positions, after one minute of operation ofrthe motor 37, the fingers 56 and 58 will simultaneously drop off the nodes of their respective cams, thus closing switches 34 and 49. Closure of the switch 34 establishes a holding circuit for energizing the motor 37, which is traced from line wire 18 through contacts 20 and 21 of the thermostat 17, wire 23, contact 24, contact 26, Wire 27, wire 32, movable contact 33 of switch 34, contact 35, Wire 36, motor 37, and wire 38 to line wire 19. It will be seen that this circuit is independent of the contacts 28 and 30 of switch 29, so that, though the contact 28 may be moved out of engagement with contact 30, the motor 37 will continue to run, once switch 34 has been closed, until that switch is reopened as the finger 56 rides onto the node of its cam 53 after completion of one full' rotation of that cam.

Closure of the switch 49 establishes an energizing circuit for the ignition unit 14, which is traced from line wire 18 through the contacts 20 and 21 of the room thermostat 17, wire 23, contact 24, contact 26, wire 27, contact 28, contact 30,. wire 46, wire 47, contact 48, contact 50, wire 51, ignition unit 14, and wire 52 to line wire 19. Thus, so long as contacts 24 and 26 remain in engagement, and contacts 28 and 30 remain in engagement, and switch 49 remains closed, the ignition unit 14 will remain energized.

The cam wheel is so proportioned and designed that the switch 49 will remain closed for five minutes. At the end of that time, the finger 58 rides onto the node of the cam 55 and, substantially simultaneously, the finger 57 drops oil the node of the cam 54. Thus, the switch 49 is opened and substantially simultaneously the switch 41 is closed. Thus, the ignition unit 14 is deenergized and an energizing circuit for the motor 13 of the stoker 12 is established, traceable from line wire 18 through contacts 20 and 21 of the thermostat 17, wire 23, contact 24, contact 26, wire 27, wire 32, wire 39, contact 40, contact 42, wire 43, Wire 44, motor 13 and line wire 19.

The cam wheel is so proportioned and designed that these conditions, in which switch 34 and switch 41 are closed and switch 49 is open, will continue for a further period of fourteen minutes to complete the twentyminute cycle of the cam wheel driven by the motor 37. Ordinarily, combustion within the chamber 11 will take place during this period of fourteen minutes, preceded by the ignition period of five minutes; and, if combustion does occur, the temperature of the smoke pipe or stack 15 will be raised sufiiciently to cause the contact 28, under the influence of the control later to be described in detail, to shift out of engagement with the contact 30 and into engagement with the contact 31.

It will be noted that such shifting of the contact 28 will not aflect either the holding circuit for the motor 37, which extends through the switch 34, or the above-traced energizing circuit for the motor 13, which extends through the switch 41, both of these circuits being independent of the contacts 28 and 30. However, when the switch 34 opens, under these conditions, the motor 37 will be deenergized, since the primary circuit therefor does extend through the contacts 28 and 30.

Movement of the contact 28 into engagement with the contact 31 establishes an energizing circuit for the motor 13, independent of the switch 41. That circuit may be traced from line wire 18 through contacts 20 and 21 of thermostat 17, wire 23, contact 24, contact 26, wire 27, contact 28, contact 31, wire 45, wire 44, motor 13, and line wire 19. Thus, once combustion has been established, the motor 13 will continue in operation for as long 'as the thermostat 17 calls for heat, unless the switch 25 opens, or the contact 28 moves out of engagement with the contact 31. As will appear from the following description, the switch 25 will be opened only if the temperature of the smoke pipe 15 exceeds a predetermined maximum, while the contact 28 will move away from the contact 31 only if the temperature of the stack 15 drops below a predetermined minimum. Thus it will be seen that the switch 29 constitutes a doublecontact switch having a normal position (as illustrated) for permitting closure of the igniter energizing circuit while temporarily preventing closure of the fuel supplying circuit, and having an abnormal position (with contacts 28 and 3t) engaged) closing said fuel supplying circuit while preventing closure of said igniter circuit.

Referring now to Figs. 2 and 3, it will be seen that the unit 59 comprises a housing 69 within which the switches 25 and 29 are enclosed. Terminals or binding posts 77, 78, 79 and provide for conveniently connecting the leads to and from the switches 25 and 29 with the several wires 23, 32, 45 and 46, as will appear hereinafter.

The housing 60 is formed to provide a base or floor 63 having lateral flanges 64, 64, for protecting a plate 61 of copper or other suitable material having a high coeflicient of heat conductivity. A sheet of heat insulating material, such as asbestos, or the like, overlies the inner surface of the plate 61, and is indicated by the reference numeral 62. The insulating sheet 62 and the floor 63 are perforated or apertured at 65 and 64, respectively, to expose a section 66 of suitable length, of the inner surface of the plate 61, to the interior of the housing 60.

A bracket 67 is suitably supported within the housing 60, and one end 68 of a bimetallic bar, indicated generally.

by the reference numeral 69, is suitably anchored upon the bracket 67. The bar 69 is bent or folded, as at 70, so that its opposite end 71 lies at a substantial angle to the position of the end 68 thereof. The parts are so proportioned and designed that, when the temperature of the bar 69 is below a predetermined minimum, the end portion 71 of said bar will lie in intimate contact with the exposed portion 66 of the inner surface of the heatconductive plate 61, so that heat may be transmitted to the end portion 71 of the bar 69 by direct conduction through the plate 61. The bar 69 is so arranged that an increase in the temperature impressed thereupon causes the end portion 71 thereof to move upwardly, as viewed in Fig. 2, thus moving away from the surface 66 of the plate 61. Obviously, initial movement of the bar end portion 71, under the influence of an increase in its temperature above the predetermined minimum, shifts said bar end portion out of contact with the plate 61, so that the transfer of any further heat to said bar end portion, further to increase its temperature, must be. by convection through the air enclosed within the housing 60.

As a consequence of this arrangement, the bar is, of course, highly sensitive to heat supplied to the plate 61 at all temperatures up to and including the above-mentioned predetermined minimum, but is much less sensitive to heat supplied to said plate, at temperatures above the predetermined minimum, after the bar end portion 71 has moved out of contact with the plate 61.

The switch 29 is provided With an actuator arm 72 which carries, at its outer end, a roller 73 resting upon the upper surface of the bar end portion 71, and yieldably held in engagement with the bar and in any suitable manner. As illustrated, the switch 29 is a conventional, double-contact, micro-switch, provided with the usual operating button 74, spring pressed outwardly; and said button bears against the actuator arm 72 to hold the roller 73 resiliently in engagement with the bar end portion 71. The parts are so arranged, of course, that when the arm 72 is in its illustrated position, the contact 28 is in engagement with the contact 30; but initial movement of the bar end portion 71 out of contact with the plate 61 will shift the roller 73, and so the arm 72, sufficiently to shift the contact 28 out of engagement with the contact 30 and into engagement with the contact 31.

The switch 25 is provided with an actuating plunger 75, disposed in the path of the movable end of the arm 72. Under normal conditions, and with the plunger 75 in its illustrated position, the contact 26 will be in engagement with the contact 24; but when the plunger 75 is moved upwardly, as the bar end portion 71 moves to its dotted line position, the movement of the plunger 75 will shift the contact 26 out of engagement with the contact 24.

The base 63, insulating sheet 62 and plate 61 are formed with a plurality of apertures 81 therethrough, for the reception of screws 82, or the like, whereby the unit 59 may be secured to the smoke pipe or stack 15, in the manner suggested in Fig. 3, with the plate 61 in intimate contact or engagement with the outer surface of the metallic smoke pipe. Preferably, one side of the housing 60 will be open, and will be normally closed by a cover 83, suitably secured in place by screws 84, or the like.

It will now be obvious that, when combustion does not exist within the chamber 11, so that the smoke pipe 15 is relatively cold, the control parts will be in the positions illustrated in Fig. l, and the bimetallic bar 69 will be in its condition illustrated in solid lines in Fig. 2. If the thermostat 17 calls for heat, the motor 37 will be energized, in the manner described above, to carry the control system through the cycle which has been described in detail. If combustion within the chamber 11 is successfully initiated, the smoke pipe will be quickly warmed, and heat will be transmitted therefrom through its metal wall, through the copper plate 61 and to the bimetallic bar end portion 71 which will be quickly affected to flex out of engagement with the exposed surface 66 of the plate 61. Such flexure of the bar will shift the actuator 72 of the switch 29 to disengage the contact 28 from the contact 30 and move it into engagement with the contact 31. Preferably, the switch 2 will be so constructed as to provide for snap action of the contact 28.

Fluctuations in the temperature of the smoke pipe, between the above-mentioned minimum and a predetermined maximum, will cause relatively slight, and rather sluggish, movements of the end portion 71 of the bar 69; and said end portion will not move far enough, under normal conditions, to cause the plunger 75 of the switch 25 to be shifted. However, if for any reason the temperature within the smoke pipe should rise to a dangerous value, the bar end portion 71 will be caused to move far enough to shift the plunger 75, thereby opening the limit switch 25 in the manner above described.

It will be clear, of course, that so long as combustion exists within the chamber 11, at a temperature suflicient to permit normal operation of the stoker, a call for heat through the thermostat 17 will not energize the motor 37 and will not energize the igniter unit 14, since the primary circuit for the motor 37 must go through the contacts 28 and 30, and since the igniter unit 14 can be energized only through the switch 49 which is open at all times except when the finger 58 is riding the lower portion of the cam surface 55. So long as the contact 28 is in engagement with the contact 31, a call for heat through the thermostat 17 merely energizes the motor 13 without affecting any other portions of the control.

While the unit 59, including the bimetallic bar 69 having its end portion 71 normally in direct engagement with the plate 61 of high heat conductivity, finds its primary utility in the system illustrated in Fig. 1, it will be clear that such a unit will be useful, also, in other systems. I presently believe that I am the first to have conceived the idea of providing a thermo-responsive element so constructed and arranged that, within a relatively low temperature range, it is subject to temperature variations transmitted thereto by conduction, while, in a relatively high temperature range, it is subject to temperature variations transmitted thereto only by convection.

I claim as my invention:

1. A thermo-responsive unit comprising a bi-metallic 6 element, a housing enclosing said element, a member subject to temperature changes and having a portion whose outer surface is exposed to such temperature changes and whose inner surface is exposed to the interior of said housing, means in said housing supporting said bi-rnetallic element in such a position that, when said element is relatively cool, a portion only of said element lies in contact with said inner exposed surface of said member, fiexure of said element in response to elevation of the temperature thereof acting to move all of said element portion out of contact with said inner exposed surface of said member, a first shiftable member disposed in said housing in the path of said element portion and actuable thereby upon movement of said element portion out of such contact, and a second shiftable member disposed in said housing in the path of said element portion and actuable thereby upon further movement of said element portion under the influence of heat transmitted thereto from said first named member solely by convection.

2. A thermo-responsive switch unit comprising a housing having a wall formed of material of relatively high heat conductivity, a first electric switch and a second electric switch mounted within said housing, a bi-metal bar, means within said housing supporting one end portion of said bar, the other end portion of said bar being disposed at a substantial angle to said one end portion and lying, when said bar is relatively cool, flatly in contact with an exposed internal portion of said wall, fiexure of said bar in response to elevation of the temperature thereof acting to shift said other end portion thereof toward said one end portion thereof and out of contact with said exposed wall portion, an actuator for one of said switches disposed in the path of said other bar end portion to be shifted thereby, as said other bar end portion leaves contact with said exposed Wall portion under the influence of heat transmitted thereto by conduction, and an actuator for the other of said switches disposed for shifting in response to further movement of said other bar end portion under the influence of heat transmitted thereto by conviction through the atmosphere within said housing.

3. In a control system for a burner including a combustion chamber, an electrically-activated i nitcr, electrically-activated means for supplying fuel to said combustion chamber, and a stack for conducting combustion products from said chamber, an energizing circuit for said igniter, an energizing circuit for said fuel supplying means, a double-contact switch having a normal position for permitting closure of said igniter energizing circuit while temporarily preventing closure of said fuel supplying circuit and an abnormal position for closing said fuel supplying circuit while preventing closure of said igniter circuit, and a normally closed limit switch dominating both of said circuits, the invention which comprises a housing having a wall formed of material of relatively high heat conductivity, means securing said housing to said stack with the external surface of said housing wall in intimate heat-conducting contact with said stack, a bi-metal bar, means within said housing supporting one end portion of said bar, the other end portion of said bar being disposed at a substantial angle to said one end portion and lying, when said bar is relatively cool, flatly in heat-conducting contact with the internal surface of said housing wall, fiexure of said bar in response to elevation of the temperature thereof acting to shift said other end portion of said bar toward said one end portion thereof and out of contact with, and away from, said housing wall, an actuator for said double-contact switch disposed closely in the path of said other end portion of said bar to be shifted thereby, upon initial movement of said other end portion out of contact with said housing Wall, whereby said double-contact switch is actuated to its abnormal position, and actuating means for said limit 7 switch comprising an actuator disposed for actuation, by movement of said other end portion of :said bar to a substantial degree away from said housing Wall, to open said limit switch.

References Cited in the file of this patent UNITED STATES PATENTS 2,008,163 Walder July 16, 1935 8 Dezotell July 13, 1937 Varley Dec. 27, 1938 Scoggin et al Apr. 1, 1941 Sahli Sept. 30, 1941 Scott et a1 Apr. 21, 1942 Eldredge July 14, 1942 Hotchkiss Oct.2,' 1945 Patent No, 2,851,971

September 16, 1.958

David To Campbell It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, lines 19 and 20, strike out "by convection and insert instead through the ambient atmosphere Within said housing line 41, for "conviction" read conveetion Signedand sealed this 18th day of November U958,

(SEAL) Attest:

KARL H o AXLINE Attesting Ofi'icer ROBERT C. WATSQN Commissioner of Patents UNITED STATES PATENT OFFKCE CERTlFICATE 0F QQRMTHUN Patent No. 2,851,971 September 1.6 1958 David "T, Campbell It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, lines 19 and 20, strike out "by convection" and insert instead through the ambient atmosphere within said housing line 41, for convieiiorr read convection Signedvand sealed this 18th day of November 1958.,

(SEAL) Attest:

KARL AXLINE 7 ROBERT C. WATSQN Attesting Oflicer Commissioner of Patents

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