US2578947A - Primary control for burners - Google Patents

Description

1951 J. J. ROTHWELL EIAL 2,578,947

PRIMARY CONTROL FOR BURNERS 2 SHEETS-SHEET 2 Filed Oct. 17, 1945 i Z 7A if E N Z Patented Dec. 18, 1951 PRIMARY CONTROL FOR BURNERS John J. Rothwell, Elkhart, and Leland B. Wagner, Goshen, Ind., assignors to Penn Electric Switch 00., Goshcn, Ind., a corporation of Iowa Application October 17, 1945, Serial No. 622,888

3 Claims.

This invention relates for burners to take the switch having a "slip" to a control structure place of the. usual stack or friction connection.

One object of our invention is to provide a combined combustion switch and safety switch which may be connected in a burner control circuit so as to deenergize the circuit as a result of combustion failure initially, combustion failure after establishment, or failure of a safety heater such as a burned-out condition thereof.

Another object is to provide a primary" control for a burner which is simple in construction and inexpensive to manufacture, and which has improved constructional and operational characteristics when compared with the burner control system shown in our Patent No. 2,367,059, issued January 9, 1945.

A further object is to provide a controller which is arranged to respond directly to the heat of combustion by exposing a bimetal element of the primary control to heat from a combustion chamber, it being unnecessary to locate the control inside a stack or inside the combustion chamber, but merely externally of the combustion chamber with an opening through the wall thereof to expose the bimetal element to the heat therein, the bimetal element responding to the combustion chamber temperature and another bimetal element responding to a safety heater, both being enclosed within a housing which assures substantially constant operating characteristics for the primary control so that it operates properly under all conditions.

Still a further object is to provide a primary control of this general character which may be either of the recycling type or of the lock-out type, requiring reset before recycling after a shut-down caused by combustion failure.

An additional object is to provide a combustion switch which utilizes a pair of bimetal elements or difierent parts of one bimetal element for response to two difierent conditions, 1) the combustion heat, and (2) the heat from an electrically energized heater, the parts being so associated in a control circuit that the desired opening of the circuit is had upon combustion failure either prior to or subsequent to combustion establishment.

With these and other objects in view, our invention consists in the construction, arrangement and combination of the various parts of our primary control whereby the objects contemplated are attained, as hereinafter more fully set forth, pointed out in the claims and illustrated in the accompanying drawings, wherein:

Fig. 1 is a plan view of a primary control embodying our present invention and showing an electrical diagram of a burner circuit in connection therewith;

Fig. 2 is a vertical sectional view on the line 2 2 of Fig. 1;

Fig. 3 is a vertical sectional view on the line 33 of Fig. 2;

Fig. 4 is a diagrammatic view similar to a portion of Fig. 2 showing the parts in the position they assume upon combustion establishment;

Fig. 5 is a similar diagrammatic view showing the position of the parts upon combustion failure;

Fig. 6 is a plan view of a modified form of the invention;

Fig. 7 is a vertical the line 'l 1 of Fig. 6;

Fig. 8 is a vertical 88 of Fig. 7.

On the accompanying drawings we have used the reference numeral II) to indicate a furnace wall or the wall of a combustion chamber, which wall has an opening 12 cut therein. Our primary control, indicated generally at PC, includes a housing It having a flange l6 secured to a plate 48, as by rivets 20, with a heat insulating gasket 22 between the two. The plate IS, in turn is secured as by screws 24 to the furnace wall I 0, with an opening 25 in the plate l8 registering with the opening I2 so that radiated and conducted heat can pass through the openings [2 and 25 into the interior of the housing l4. Surmounting the housing I 4 is a second housing 26 adapted to contain switch mechanism, as will be hereinafter described. A cover 21 is provided for the housing 26 and this cover has been omitted from Fig. 1.

The switch housing 25 serves as a support for a bimetal element 13, a shield S and a heater H, all of which depend from the housing 26. Within the housing 26 a permanent magnet 28 is supported for snap-acting cooperation with an armature 30, which armature is secured, as by screws 32, to a central section 34 of the bimetal element B.

The section 34 is shown formed in four strips. The bimetal element B has two other sections 36 formed in two strips. The entire bimetal element is thus in the form of a W, having two connecting portions 38 at thebottom for the sections 34 with relation to the sections 36. A pair of bars 40 is then secured along the bottom of the bimetal element for reinforcing it. The upper ends of the sections 36 are anchored to a bracket 42, as by screws 44.

sectional view thereof on and sectional view on the line The armature 30 carries a movable contact 48 for coaction with a stationary contact 50 mounted on a bracket 52. The bracket 52 is connected by a strap 54 with a screw 56 to which a bracket 58 is secured for supporting the heater H and for connection to one end of the resistance wire in the heater. The other end of the resistance wire is connected to a second bracket 60 which, in turn, is connected to a screw 62 and a strap 64 extends from the screw 62 to a terminal 66. A second terminal 68 is provided on the bracket 42, which bracket supports the bimetal element B so that a circuit can be traced from the terminal 66 through the elements 64, 62, 60, H, 58, 56, 54, 52, 50, 48, B, and 42 to 68. This places the contacts 48 and 50 in series with the heater H, and the two are in a control circuit, as shown in Fig. l, which includes, in series, a room thermostat RT, a secondary S of a step-down transformer T, and a relay coil RC. The circuit also includes current supply wires and 12 for a burner motor BM, its ignition mechanism Ign and for the primary P of the transformer T. The burner motor EM and the ignition mechanism Ign are controlled by a motor switch MS which is normally open and closes in response to the relay coil RC being energized.

In the combined combustion and safety switch shown in our patent hereinbefore' mentioned there was no casing for the bimetal elements, and it was found that they were sometimes erratic in action. This was particularly true due to the temperature ambient to the bimetal elements varying as by differences in the draft through the furnace, and passing air currents surrounding the furnace. It will be noted in the present application that we have entirely enclosed the bimetal element B within the housing [4, with the exception of the opening 25.

This places both portions 34 and 36 of the bimetal element in the same ambient temperature, and that ambient temperature is isolated from the surrounding atmosphere while, at the same time, both sections of the bimetal are subject to the furnace temperature through the opening 25. It is necessary, however, that the bimetal element section 34 respond mainly to heat from the heater H, whereas the element sections 36 respond mainly to the heat of combustion. This is accomplished by leaving the sections 36 unobstructed for direct radiation of heat from the interior of the combustion chamber while shielding the element section 34, as by the shield S. This shield has a wall 14 facing the heat from the combustion chamber. The wall 14 has a pair of side wings 16 to isolate the bimetal section 34 from direct rays of heat from the furnace. However, both bimetal element sections 34 and 36 are subject to the general temperature within the housing l4 so that regardless of whether that temperature is low, as when starting the furnace, or high, as after it has operated a considerable time period, both bimetal elements in so responding compensate/for the ambient temperature in which they are located, as will be hereinafter more fully described.

The type of control shown in Figs. 1, 2 and 3 has a snap-acting switch which returns to closed positions after a flame failure when the parts cool down again. It is more desirable, however, to have the switch lock out so that whatever caused the flame failure can be remedied, and the switch then reset.

In Figs. 6, '7 and 8 we show a modified form of the invention for accomplishing this result. In

d place of an armature and magnet, snap action is secured by a toggle mechanism consisting of a toggle lever l8 pivoted by means of knife edge pivots at 86 to a stationary vertical flange 82. A toggle spring 85 connects a transverse portion 86 of the toggle lever 18 with a notched portion 88 of the vertical flange 82, and the toggle lever is normally in the position shown in Fig. 6 against a stop screw 30.

In place of the armature 36 an extension 92 from the bimetal section 34 is adapted to contact the right-hand end of the toggle lever 56 and move it upwardly in Fig. 6 for causing an adjusting screw 94 carried thereby to slide a pin 66 lengthwise through a perforation 98. The pin 96 thereupon engages'a leaf spring 566 which has the movable contact 48 mounted thereon and normally engagedwith the stationary contact 55.

The parts 34, 48 and 50 correspond to those in the first three figures of the drawing, and other parts of this form of structure also correspond to parts of the first three figures, and, accordingly, bear the same reference numerals. The contact 50 is mounted on leaf spring 12. The spring I02 and the spring I66 are connected in the circuit, as in series with the heater H, in a manner similar to that already described.

When the toggle lever 18 is rocked counterclockwise from the position shown in Fig. 6, due to combustion failure, it stays in that position, thus holding the contact 66 separated from the contact 50. The trouble must then be remedied and the device reset. Reset is accomplished by means of a slidable reset bar Hi4 having a pair of ears M6 to engage a flange 568 on the pin 36. The pin can thereby be pushed downwardly in Fig. 6 to return the toggle lever 18 to its original position shown by solid lines. At the same time. an ear H6 on the reset lever Hi6 engages the leaf spring I02 to hold the contact 50 away from the contact 48 to prevent the possibility of manually holding the contacts closed while a dangerous condition of the furnace prevails. A spring W9 is provided for returning the reset-lever 866 to its initial position.

PRACTICAL OPERATION Normal burner operation In the operation of our invention, when the parts are in the cold position of Figs. 1 and 2, the contact 48 is held under pressure against the contact 50 due to the relative settings of the mounting bracket for the bimetal element B and the desired tension in the bimetal for contact pressure. The secondary circuit of the transformer is thereby ready for operation whenever the room thermostat RT closes. Upon closure of the room thermostat a circuit may be traced from the top of the secondary coil S through the room thermostat, the heater H and the relay coil BC in series, thereby closing the motor switch MS so that the burner motor BM and its ignition mechanism will operate.

Energization of the heater H causes the bimetal element portion 34 to become warped, as shown by solid lines in Fig. 4, the position of the heater in relation to the bimetal, and the heat transfer relation of the heater being so selected that the warping of the bimetal element is com paratively slow. The heat flow is indicated by arrows a.

In the meantime, burner operation has been successfully established and the radiant heat flow from the combustion chamber, indicated by the arrows 1), causes heating of the bimetal element sections 36 so that they too warp to approximately the same curvature as the section 34 whereupon the composite element B assumes the dotted position of Figure 4. At the same time both bimetal element sections are heated by heat from the furnace, both sections being within the housing l4 are thereby subject to the general temperature within this housing as it rises in proportion to a rise of furnace temperature which merely increases the dotted curvature in Figure 4 all the way up to the point where the temperature becomes stabilized without changing the position of the upper end of the section 34. We have found that location of the two bimetal element sections in the same ambient temperature, and that temperature stabilized as by complete enclosure within a housing, is necessary for proper operation at all times, and have further found that the housing surrounding the bimetal element sections should be completely opened for the reception of direct heat rays from the interior of the furnace without any intervening wall of glass or the like which might become smoked and cut down heat transmission. As to the bimetal element sections 36, they operate best when blackened, as they then have maximum heat absorption qualities and operate most efiiciently.

In addition to the general subjection to ambient temperature within the housng I4, the sections 36 of the bimetal are definitely responsive to radiant heat from the combustion chamber. The 'combustion heat transfer to the sections 36, as indicated by the arrow b, causes these sections likewise to warp so that the upper end or armature 30 of the bimetal remains in positionfor keeping the contacts 48 and 50 closed. The magnet 28, acting on the armature 30. also aids in retaining a closed circuit and increases the initial contact pressure in addition to the tension in the bimetal.

Thus, during normal burner operation the contacts 48 and 50, which may be termed safety contacts are retained closed, and, subsequently, when the room thermostat opens the relay coil is deenergized to thereby open the motor switch and stop the burner. The bimetal B then cools down, returning to its original position, as in Fig. 2. When the burner on periods are extended both bimetals will warp to a further curvature, as shown by dotted lines in Fig. 4, thus still maintaining the contacts closed, and since both bimetal sections are subject to the furnace temperature, both will be warped substantially equal. Their relative sizes and the size of the shield S may be varied to secure the desired results.

Failure of combustion to be established Referring to Fig. 5, if combustion does not occur in the normal manner the bimetal element sections 36 will remain in their cold positions while the bimetal element section 34 will move to its hot position, due to energization of the heater H. This will take preferably about a minute or so, although the time does not have to be as long as it takes the usual safety switch in a stack switch installation to drop out. The room thermostat circuit is now opened across the safety switch contacts 48 and 50 so that the relay coil is deenergized, thus opening the motor switch.

After a time period, predetermined by the length of time it takes the heater H and the bimetal element section 34 to cool down, the con- 6 trol circuit will be reestablished, thus providing a purging period and thereby permitting an at tempt at another start of the burner.

In the form of device shown in Figs. 6 and 7, after the contacts 48 and 50 are separated they will remain so, as return of the element 92, due to cooling down of the bimetal element section 34, merely causes the element 92 to walk away from the toggle lever 18. The toggle spring being over-center in the opposite position from that shown in Fig. 6 will cause the contacts to remain open until such time as they are reset by pushing in on the lever I04 after the trouble has been remedied.

Combustion failure after establishment Referring to Figs. 4 and 5, wherein Fig. 4 shows combustion having been established, if there is a subsequent failure of combustion the bimetal element sections 36 will straighten out again as to the position of Fig. 5, thereby opening the safety switch contacts 48 and 50 for shutting down the burner for a purging period, or with the construction of Figs. 6 and 7 for a lock-out. The flame failure, of course, permits the combustion chamber to cool down and the bimetal element sections 36 thus become cooled while the section 34 remains heated due to continued energization of the heater H. Thus the contacts 48 and 50 take the place of both the safety switch contacts and the combustion switch contacts in the usual type of stack switch hav ing a thermal responsive element in the stack and an individual safety switch with its separate contacts, the safety switch including a heater which is not connected with the combustion switch except in the electrical circuit. In our device, on the other hand, the bimetal element is so arranged that it responds both to a heater and combustion temperature in such manner that a single set of contacts serve as a control in response to combustion and a safety switch in response to current through a heater. Our primary control herein disclosed is therefore, in effect, a combined combustion switch and safety switch in which the contacts 48 and 50 are separated as a result of a cold combustion chamber and a hot heater. Whenever these two events occur at the same time the burner is shut down. whereas during normal cycling of the burner the contacts remain engaged and are never separated. Separation occurs only when there is either an initial combustion failure or a combustion failure subsequent to establishment thereof. Our arrangement is such that we have the primary control responsive to combustion chamber temperatures from a point exterior of the combustion chamber where the temperatures range only from 70 to 700 F. Our control entirely eliminates a slip connection and is so designed as to combine a warp type of safety switch with a combustion responsive element so as to use a single set of contacts, which contacts are maintained in proper relation to each other, regardless of temperature ambient to the bimetal element sections. The bimetal may be a single piece made in sections, as disclosed, or made of two or more pieces connected together to secure the same results and may warp toward the heater and the combustion chamber instead of away from them, as disclosed in Figs. 4 and 5.

We have found that rather wide variations in combustion chamber temperatures and heater temperatures do not materially affect operation of the primary control, providing the bimetal aerate? long as that ambient is stabilized as by being open to the interior of the combustion chamber. The housing for the bimetal sections eliminates the possibility of stray air currents and changes element in direct communication with the in-v terior of the furnace without any intervening 'windowsoi glass or the like, all possibility of failure of operation due to reduction in heat flow from thecombustion chamber to the bimetal element is eliminated, and regardless of what temperature the furnace attains, the bimetal element is always self-compensating, as both sections 39 and 36, being subjected to the furnace temperature, warp substantially equally in spite of the element '34 being shielded by the shield S from the direct rays of heat from the combustion chamber. It is a simple matter to connect the controller into the circuit for controlling -it in a manner similar to that had from a regulation stack switch. 7

Some changes may be made in the construction andarrangement of the parts of our burner control system without departing from the real spirit and purpose of our invention, and it is our intention to cover by our claims any modified forms of structure or use of mechanical equivalents which may be reasonably included within their scope.

We claim as our invention:

1. A primary control for burners comprising a bimetal element having a pair of side-by-side sections connected together at one end, the other end of one section being anchored and the other end of the other section constituting an actuating element, a combustion switch having switch contacts which are openable by said actuating element, an electric heater, one of said bimetal element sections being responsive to heat from said electric heater, and a common housing for both of said bimetal element sections whereby both sections are subject to the same ambient temperature therein, said housing having an opening through which heat may be radiated to actuate the other of said bimetal element sections, and a shield in said housing between said opening and said first bimetal element section.

2. In a burner control, a combustion switch, a heating element, said combustion switch comprising a pair of thermal elements arranged side-byside in substantially the same plane, connected sections are both in the same ambient, and as together at one end and the other end of each being anchored and free respectively, said combustion switch having contacts controlled by said free end, a housing for both of said bimetal elements and having an opening, a shield for one oisaid bimetal elements to shield it from direct rays through said opening, said heating element being located adjacent said one of said bimetal elements to heat the same predominantly with respect to heat through said opening, said elements when responding to a normal burner operating condition moving in the same direction with said contacts remaining closed, heating of said heating element and cooling ora cold condition through said opening moving said bimetal elements unequally and thereby effecting separation of said contacts.

3. In a primary control for burners, a combustion switch comprising a pair of side-by-side thermal elements, contacts controlled thereby, a housing having an opening, both of said thermal elements being housed therein for response to temperature therein, one of said thermal elements being located to have an unobstructed and direct path through the air from said opening to the element, obstructing means between the other element and said opening, and a heating element located adjacent said other element to heat the same when energized with an amount of heat which is in addition to that indirectly absorbed by the thermal-element through said opening.

JOm J. ROTHWELL. 1 i B. WAGNER.

REFERENCES (CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,576,056 Liefke Mar. 9, 1926 2,041,559 Marks May 19, 1936 2,095,846 Westendorp Oct. 12, 1937 2,098,383 Furlong Nov. 9, 1937 2,159,392 McCabe May 23, 1939 2,162,098 McCabe June 13, 1939 2,227,901 Hageman Jan. '7, 1941 2,267,463 Hood et a1. Dec. 23, 1941 2,281,319 Newell Apr. 28, 1942 2,284,383 Elmer May 26, 1942 2,302,399 Stimson Nov. 17, 1942 2,367,059 Rothwell et al Jan. 9, 1945

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