US2309317A - Burner control - Google Patents

Description

Jan. 26, 1943. G. HOLMES 2,309,317

BURNER CONTROL Filed May 29, 1940 INVENTOR Gifford I. Holmes ATTQRN EY Patented Jan. 26, 1943 BURNER CONTROL Gifford 1. Holmes, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Application May 29, 1940, Serial No. 337,852

15 Claims. (Cl. 158-28) The present invention relates to burner controls and more particularly to a novel control circuit and mechanism whereby a high degree of safety is obtained.

In burner control circuits it is customary to provide some combustion responsive device which controls a circuit upon the occurrence of combustion when igniting, or upon a flame failure when the burner is in operation. In most instances these devices are adapted to complete a circuit when combustion occurs and maintain the circuit for normal operation of the burner. In many instances these contacts freeze or weld together, in which case, if flame failure occurs there is no protection against flooding the vicinity of the burner with highly combustible fuel. Not infrequently, upon starting the burner after such a failure, a serious explosion or fire will result.

It is also customary practice to provide relay mechanisms which may operate on either high or low voltage to control the burner motor circuit. These relays comprise many parts and add considerably to the cost of equipment. Safety switches are frequently combined with the combustion device or the relay, also adding to this cost.

A prime object of the present invention is to provide a combined relay and safety switch for a burner control.

Another object is to provide a combustion responsive switch and circuit which will not cause an unsafe condition if the contacts thereof should stick or weld in closed position.

A further object is to provide a burner circuit wherein a closed cold stack switch is combined with a thermal relay and safety switch.

Other objects and advantages of the present invention will be in part obvious and in part pointed out in the accompanying specification and claims.

For a complete understanding of my invention reference will be made to the drawing, the single figure of which shows a diagrammatic burner control system.

In the drawing, a burner control motor 5, which may be a motor for an oil burner or a gas valve motor, and an ignition means 6 are under the control of a condition responsive device II). This condition responsive device may take the form of a thermostat comprising a bimetallic coil II, a. contact blade [2, and a stationary contact I3 which cooperates with the contact blade I2 in controlling an electrical circuit. A combustion responsive device generally indicated at ll is also provided in control of this electrical circuit and may take the form of a device which is responsive to the radiant heat of the flame or of the conducted heat from the flame, or other conventional device, and is diagrammatically shown as comprising a switch blade l5 which cooperates with a stationary contact I6 which contact and blade engage each other upon relatively cold temperature. This contact is adapted to be opened when the heat rises in response to combustion and closed in the absence of combustion. The low voltage circuit which the condition responsive control device l0 and the combustion responsive device ll are in control of originates fro a transformer II which comprises a high vo tage primary I8 and a low voltage secondary iii.

A combined heat motor relay and safety switch is generally indicated by the reference character 20. The heat motor comprises a heater 2| which may be wrapped around or suitably arranged in proximity to a bimetallic strip 22 which may be suitably secured to a bracket 23. Th heater 2| and the bimetallic element 22 cooperate to cause the bimetallic element 22 to warp towards the right upon energizatlon of the heater 2| and to warp towards the left upon deenergizaton thereof. The bimetallic strip 22 may be pro 'ded with an opposed bimetallic strip to compensate for changes in the ambient temperature in a conventional manner which is well known in the art and therefore not shown. The upper end 24 of the bimetallic strip 22 engages an insulating abutting block 25 which is secured to a contact blade 26. The contact blade 26 is suitably secured to a mounting bracket 21. The blade 26 carries a contact 28 which is in cooperative relationship to a contact 29 carried by a switch blade 30 that is suitably secured to a mounting bracket 3 I. These switch contacts 28 and 28 are held in their closed position as long as the end 24 of the bimetallic strip 22 remains in abutting engagement with the insulating block 25. When the end 24 is moved from beneath the block 25 the switch blade 26 will move downwardly to separate the contacts 28 and 29. A resetting mechanism is shown as comprising a push rod 36 which when pushed upward raises the insulating buttons 31 and 38 to lift theswitch blades 26 and 30 and permit the end 24 of the bimetallic strip 22 to move beneath -the insulating block 25 to reset the device after it has been tripped. The insulating buttons 31 and 38 are so arranged in relationship to the switch arms 26 and 30 that the contacts 28 and 28 will be held in open position during this resetting operation.

The bimetallic strip 22 also serves as a relay to open and close a mercury switch 45 carried upon an arm 4| that is suitably pivoted at 42. A connecting link 43, which is diagrammatically shown as a dotted line, connects the arm 4| to the bimetallic strip 22. It will be seen that when the arm 4| is rotated toward the right, which will occur when the bimetallic strip 22 is heated, that the mercury switch 40 will be rocked in a counterclockwise direction to cause the mercury therein to flow toward the left to bridge contacts 44 and 45 and cause energization of the motor 5 and ignition means 5. When the bimetallic strip 22 cools, themercury switch will be rocked in a clockwise direction to unbridge the electrodes 44 and 45.

A pair of oppositely facing contacts 55 and 5| are mounted on the bimetallic strip 22 by flexible arms 52 and 55, respectively. The contact 55 cooperates with a stationary contact 54 which is closed when the bimetallic strip 22 is in its cold position (as shown). The contact 5| cooperates with a stationary contact 55 which is closed when the bimetallic strip 22- is heated. The contacts 55 and 5| are so arranged in relationship to the stationary contacts 54 and 55, respectively, that the contact 5| will engage the contact 55 before the contact 50 disengages the contact 54. As will be hereinafter more particularly pointed out, the contacts 50 and 54 are adapted to intermittently make and break, or fry, to energize and deenergize the circuit to the heater 2|.

Electrical energy for consumption by the motor 5 and the ignition means 5 as well as for the low voltage control circuit is led from some suitable source of supply, not shown, through the line conductors 50 and 5|. A circuit for the primary winding 8 of the transformer may be traced as follows: from the line conductor 50 through wire 52, contacts 29 and 25 of the safety switch 25, wire 53; primary windin l5 of the transformer I1, and wire 54 to the other line conductor 5|. A circuit for the motor 5 and ignition means 5 may be traced from the line conductor 50 through wire 52, contacts 29 and 28 of the safety switch 20, wire 55, electrodes 44 and 45 of the mercury switch 40 and wire 55 to the motor and ignition means, wires 51 and 58, and wire 54 to the other line conductor 5|.

Operation With all of the parts in the position shown the space thermostat I is in its satisfied or warm position and the combustion responsive device I4 is in its cold position. Assuming now that the space temperature falls and the contacts i2 and I3 are closed, an energizing circuit for the heater 2| may be traced as follows: from the secondary I! of the transformer I! through the conductor 15, contacts l2 and I3 of the thermostat I0, conductor 1|, conductor I2, switch arm l5, contact l5, conductor I3, heater 2|, conductor I4 back to the other side of the transformer secondary l5. When this circuit is completed the heater 2| will generate heat which will cause the bimetallic strip 22 to warp toward the right. Upon warping toward the right the arm 4| which carries the mercury switch 45 will be moved toward the right which will cause the mercury within the tube to bridge the electrodes 44 and 45. With these electrodes bridged the burner motor and ignition means will be placed into operation through the circuit previously traced. When the bimetallic strip 22 moves toward the right the contact 5| will engage the contact 55.

It is necessary for these contacts to engage before the switch blade I5 disengages the contact II in the combustion responsive device |4. If combustion takes place properly the switch arm l5 will move toward the left to its hot position to break the connection with the contact It. With this circuit broken an energizing circuit for the heater 2| may be traced as follows: from the transformer secondary I! through conductor 15, thermostat Ill, conductor H, conductor 15, stationary contact 55, contact 5|, flexible arm 52, bimetallic strip 22, flexible arm 52, contact 55, stationary contact 54, conductor 15, the heater 2|, and the conductor 14 back to the other side of the transformer secondary II. It will be noted that this energizing circuit for the heater 2| is dependent upon closure of both of contacts 5| and 55, and 50 and 54. Continued energization of the heater 2| will cause still further deflection of the bimetallic strip 22 toward the right. After the contacts 5| and 55 are in engagement the flexible arm 55 may bend toward the left to permit further movement of the thermostatic strip 22 toward the right. After a predetermined movement in which the contacts 55, 54 and 5|, 55 overlap, the contacts 50 and 54 will separate to break the energizing circuit above traced for the heater 24. When this circuit is broken the bimetallic strip 22 will begin to cool to move back toward the left and thus reengage the contacts 55 and 54. It is seen therefore that the contacts 50 and 54 will intermittently make and break to energize and deenergize the heater 2| when combustion properly takes place and the contacts l5 and I5 within the combustion responsive element l4 are open. Under these proper operating conditions with the bimetallic strip 22 oscillating between these heater control contacts, the upper end 24 of the strip 22 will remain beneath the insulating block 25 which maintains the safety switch contacts 25 and 29 in engagement. Also when the operation is proper the electrodes 44 and 45 of the mercury. switch 45 will be maintained in closed position by this oscillating movement. When the contacts i2 and 12 of the thermostat l5 separate, the control circuit will be broken and the bimetallic strip 22 will cool down and move back to the position shown in the drawing, thus breaking the motor and ignition circuit.

Assuming now that the thermostat ll closes its contacts I2 and II and combustion does not take place due to ignition failure, in this event the contacts l5 and I5 of the combustion responsive device M will remain in closed position. With the combustion responsive device remaining in this position a continuous circuit for the heater 2| may be traced as follows: from the secondary of the transformer ll through conductor 15, thermostat l0, conductors II and I2, contacts i5 and I5 of the combustion responsive device l4, conductor ll, heater 2| and conductor 14 back to the other side of the secondary ll. Because no combustion occurs contacts i5 and I5 will remain closed and the heater 2| will be continuously energized through this circuit and not intermittently made and broken by the action of the contacts 50, 5|, 54, 55 which are carried by the bimetallic strip 22. The strip 22 will be heated up to such an extent that the upper end 24 will move toward the right and out of engagement with the abutting block 25, thus permitting the safety switch contacts 25 and 25 to separate. When these contacts separate the circuit from the line wire 50 through conductor 5| will be opened and therefore there can be no circuit to the primary of the transformer nor to the motor or ignition means 6 until the safety switch has been reset by manually operating the resetting mechanism 35. Therefore it is seen that, when the device has gone out on safety as a result of failure of ignition, manual attention must be given to the system before the system can be restarted.

It will be noted that, if the contacts l5 and |6 do not close upon cooling of the combustion responsive device H, the heater 2| cannot be energized to start the burner motor 5. Also, if the contacts l5 and i6 should freeze, or weld, together, the heater 2| would remain energized to cause the safety switch to trip open. It is seen therefore that, whether the combustion responsive device i4 fails to function properly either on heating or cooling, the burner motor 5 will not be operated to cause a hazardous condition to result.

Assuming now that combustion has taken place but there is a combustion failure or a flame failure and the room thermostat I0 is not satisfied and the contacts l2 and I3 remain in closed position. From the previous explanation of normal operation it will be understood that the contacts 50 and 54 which are carried by the bimetallic strip 22 have been oscillating at some predetermined intermittent position to maintain the upper end 24 of the strip 22 in abutting engagement with the insulating block 25 as well as maintaining the energizing circuit through the switch for the motor 5 and the ignition means 6. When a flame failure occurs the combustion responsive device it will cool off and cause engagement of the contact arm IS with the stationary contact Hi. When these contacts are made a circuit for the heater may be traced from the secondary of the transformer I9, conductor 10, thermostat l0, conductors II and 12, contact arm l5, contact I6, conductor 13, heater 2| and conductor 14 back to the other side of the transformer secondary l9. This will result in continued, rather than intermittent, energization of the heater 2| and will cause the bimetallic strip 22 to warp toward the right out of engagement with the abutting block 25 to permit the safety switch contacts 28 and 29 to separate thus shutting down the system. Therefore it is seen that in the event of flame failure also, manual attention must be given to the system before it may be restarted.

While I have shown one form which my combined relay and safety switch may take, it will be obvious that many modifications which make use of the principles disclosed in the embodiment shown will occur to those skilled in the art. It

is therefore to be understood I am not to be limited only by that form shown and described but by the spirit of the appended claims.

I claim as my invention:

1. In a fuel burner system, in combination, a burner motor for operating means for delivering combustible fuel to a burner, a thermostat responsive to the temperature in a space which is heated by said burner, timing means controlled by said thermostat, switch means operated by said timing means for controlling the operation of said burner motor, a normally closed biased to open safety switch in circuit with said burner motor, said safety switch being maintained in closed position by said timing means when said burner is operating properly, combustion responsive means including closed cold contacts in setiming means in a manner to cause said safety switch to be opened in the event of ignition or flame failure within said burner, and means maintaining 'said timing means in position to maintain operation of said burner motor upon the establishment of combustion and the resultant opening of the said closed contacts.

2. In a. fuel burner system, in combination, a burner motor, an electric circuit therefor, a movable control switch in control of said circuit, a thermally warpable member for operating said switch, a heater adjacent said member for causing warping thereof, a thermostatic switch in control of said heater, 9. pair of-cooperating contacts carried upon opposite sides of said warpable member, said contacts cooperating with said thermostatic switch for causing said member to intermittently energize and deenergize said heater to thereby cause said member to maintain said control switch in energizing position, and a closed cold combustion switch also in control of said heater.

3. In a burner control circuit, in combination, a burner motor, an electric circuit therefor, a motor switch in said circuit, timing means for controlling said switch, a biased open safety switch held closed by said timing means, means including heating means for causing said timing means to close said motor switch, combustion responsive means cooperable with said last means for controlling the operation of said timing means, contact means carried upon opposite sides of and moved by said timing means, fixed contacts cooperable with said contact means and said heating means for maintaining said motor switch and said safety switch closed, and combustion responsive means for rendering said timing means operative and inoperative.

4. In a heating system, in combination, a bumer motor for operating means for supplying combustible fuel to a burner, an electric circuit therefor, an oscillatable switch in control of said circuit, a thermal motor including a warpable member and a heater for oscillating said switch ries with said timing means for controlling said to energize and deenergize said motor, a normally closed biased to open safety switch in circuit with said burner motor held closed bysaid warpable member, an energizing circuit for said heater, a closed cold temperature responsive control switch in control of said energizing circuit, a closed cold combustion switch in said energizing circuit in series with said control switch for initiating operation of said burner motor by energizing said heater, and intermittently engageable electrical contact means movable by said warpable member for intermittently energizing and deenergizing said heater to maintain said burner motor in operation, said combustion switch upon continued closure being adapted to cause said heater to remain energized to heat said warpable member sufficiently to move said member so as to permit said safety switch to open.

5. In a heating system, in combination, a timer, an electric heater, a circuit for energizing said heater, a condition responsive controller in con trol of said circuit, said heater upon energization delivering energy to said timer to produce a timed movement thereof from an initial position through an intermediate range of movement to a predetermined limit position, a closed cold combustion switch also in control of said circuit and cooperable with said condition responsive controller to initiate operation of said heater; fuel supplying means, a. circuit therefor, a first switch in control of said circuit, a second normally closed biased to open safety switch in said circuit, said safety switch being maintained closed by said timer when said timer is in its initial or intermediate range of movement, but not when in its limit position where said safety switch will be permitted to open to deenergize said circuit, and a pair of contacts operated by said timer for energizing and deenergizing said heater to maintain said timer in said intermediate range of movement.

6. In a heating system, in combination, a timer, an electric heater, a circuit for energizing said heater, a first condition responsive switch in control of said circuit, said first switch having an active closed circuit position and an inactive position, a combustion switch in said first switch, said combustion switch being responsive to the presence of a condition incident to combustion and having an active closed circuit position when, the condition is absent and an inactive position when the condition is present, said two switches cooperating in their active positions to cause energization of said heater, and switch means moved by said timer and cooperable with said first switch after said second switch has opened in response to the establishment of combustion for controlling said heater after said heater is energized.

7. In a heating system, in combination, a timer,

an electric heater, a first circuit for energizing said heater, a first condition responsive switch in control of said first circuit, said first switch having an active closed circuit position and an inactive position, a second switch in said first circuit with said first switch, said second switch being responsive to the presence of a condition and having an active closed circuit position when the condition is absent and an inactive position when the condition is present, said two switches cooperating in their active positions to initiate energization of said heater; a second circuit for energizing said heater, switch means moved by said timer and cooperable with said first switch for controlling said second circuit after said heater is energized; said switch means comprising a first contact in said second circuit which is engaged subsequent to the initial energization of said heater, and a second contact in said second circuit in juxtaposed relationship to said first contact, said second contact being adapted to alternately energize and deenergize said heater after said second switch opens.

8. In a heating system, in combination, a timer, an electric heater, a first circuit for energizing said heater, a first condition responsive switch in control of said first circuit, said first switch having an active closed circuit position and an inactive position, a second switch in said first circuit with said first switch, said second switch being responsive to the presence of a condition and having an active closed circuit position when the condition is absent and an inactive position when the condition is present, said two switches cooperating in their active positions to initiate energization of said heater, a second circuit for energizing said heater, switch means moved by said timer and cooperable with said first switch for controlling said second circuit after said heater is energized; said switch means comprising a first contact in said second circuit which is engaged subsequent to the initial energization of said heater, and a second contact in said second circuit in juxtaposed relationship to said first contact, said second 'contact being adapted to alternately energize and deenergize said heater said circuit with after said second switch opens; a burner motor. a circuit for energizing said motor, an oscillatable switch moved by said timing means in control of said circuit, and connecting means for causing energization of said circuit when said first and second switches are in their active positions.

9. In combination, an electric switch, a thermal motor movable when heated in a direction to open said switch, a single heater therefor, a first energizing circuit for said heater, a pair of condition responsive means in series with each other for energizing said first circuit; a pair of contacts operated by said thermal motor, and a second energizing circuit for said heater, said second circuit being controlled by one of said condition responsive means in series with said pair of contacts.

10. In combination, an electric switch, a thermal motor movable when heated from an initial position through an intermediate range of movement to a limit position wherein said switch will be opened, a heater for said motor, first and second energizing circuits for said heater, a first condition responsive device in control of both of said circuits, a second condition responsive device also in control of said first of said circuits, said first circuit when energized causing said thermal motor to move to said limit position to thereby open said switch, and control means operated by said thermal motor also in control of said second of said circuits, said second circuit being intermittently energized by said control means to cause said motor to remain in said intermediate range of movement when said first circuit is deenergized.

11. An automatic burner control system comprising in combination, means controlling the delivery of fuel to a burner for combustion, a timer in control of said fuel delivery means, said timer having a deenergized position in which said fuel delivery means is inoperative, a main switch, a closed cold combustion switch, means including said main switch and closed cold combustion switch for energizing said timer to cause it to move from its deenergized position to a second position in which it renders said fuel delivery means operative and later to a third position in which it again renders said fuel delivery means inoperative, and means operable by said timer in the event that said combustion switch opens while said timer is in its second position, for limiting the delivery of energy to said timer to an amount just sufiicient to maintain it in its second position.

12. An automatic burner control system comprising in combination, means controlling the delivery of fuel to a burner for combustion, a timer in control of said fuel delivery means, said timer having a deenergized position in which said fuel delivery means is inoperative, a main switch, a closed cold combustionswitch, means including said main switch and closed cold oombustion switch for energizing said timer to cause it to move from its deenergized position to a second position in which it renders said fuel delivery means operative and later to a third position in which it again renders said fuel delivery means inoperative, and switch means operated by said timer in the event that said combustion switch opens before said timer moves into its third position, said switch means alternately making and breaking an energizing circuit to said timer to maintain said timer in its second position.

13. A fluid fuel burner control system comprising in combination, means controlling the delivery of fuel to a burner for combustion, a timer, electrical means for energizing, said timer, a main switch, a closed cold combustion switch, means including said last named switches for energizing said timer to cause it to move from its deenergized position to a second position in which it renders said fuel delivery means operative to deliver fuel to said burner, third switch means closed by said timer when it is in its deenergized position, fourth switch means closed by said timer as it moves toward itssecond position, and means including said third and fourth switches for energizing said timercindependently of said combustion switch which opens when combustion has been established.

- 14. A fluid fuel burner control system comprising in combination, means controlling the delivery of fuel to a burner for combustion, a timer, electrical means for energizing said timer, a main switch, a closed cold combustion switch, means including said last named switches for energizing said timer to cause it-to' move from its deenergized position to a second position in which it renders said fuel delivery means operative to deliver fuel to said burner, said timer moving to a third position upon continued energization in which it again renders said fuel delivery means inoperative to deliver fuel, a. third switch closed by said timer when it is in its deenergized position, a fourth switch closed by said timer as it moves to its second position, means including said third and fourth switches for energizing said timer independently of said combustion switch, said timer alternately opening and closing said third switch to alternately deenergize and energize itself provided said closed cold combustion switch is open, whereby said timer remains in its second position so long as combustion is present.

15- A fluid fuel burner control system comprising in combination, means controlling the delivery of fuel to a burner for combustion, a timer, electrical means for energizing said timer, a main switch, a closed cold combustion switch, means including said last named switches for energizing said timer to cause it to move from its deenergized position to a second position in which it renders said fuel delivery means operative to deliver fuel to said burner, said timer moving to a third position upon continued energization in which it again renders said fuel delivery means inoperative to deliver fuel, a

- thereby rendering said fuel delivery means inoperative, and means preventing said timer from again rendering said fuel delivery means operation without manual intervention.

GIFFORD I. HOLMES.

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