US2196442A - Burner control system - Google Patents

Description

April 9, 1940.

M. J. MAYNARD BURNER CONTROL SYSTEM Filed Jan. 21, 1938 I a; a1 OVERLAPPING ON 8a zsmsssgxsswz a .9; g- TEMPERATURE FALL- I OVERLAPPING 0N TEMPERATURE RISE.

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lNgENTOR ATTORN EY Patented Apr. 9, 1940 I UNITED STATES PATENT OFFICE Application January 21, 1938, Serial No. 186,123

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This invention relates to a burner control system and more particularly to one employing means for checking the ignition.

It is quite common with fluid fuel burner control systems, particularly oil burner control systems, to provide an electrical ignition means for igniting the fuel. This means usually takes the form of a high voltage circuit including spaced electrodes between which a spark occurs upon energization of the high voltage circuit. It is highlydesirable that the oil burner or other fuel feeding means not be placed into operation until such time as a proper spark occurs across the ignition electrodes. Accordingly, various arrangements have been proposed from time to time to prevent operation of the fuel feeding means until the ignition means is operating properly. One such arrangement is disclosed in the application of Willis H. Gille, Serial No. 39,700, filed September 9, 1935. In the arrangement of this application, means is utilized which is responsive to the high frequency current flow in the ignition circuit adjacent to the spark gap. While the arrangement of the above mentioned Gille application was highly satisfactory as far as operation was concerned, the apparatus employed electronic tubes and other complicated equipment which unduly added to the expense of the control system and necessitated more frequent service costs by reason of the limited life of the electronic tubes employed therein.

An object of the present invention is to provide a spark checking arrangement for a burner control system in which a circuit resonant to the high frequency current accompanying a proper spark is connected in series with the spark gap closely adjacent thereto and in which the flow of fuel to the burner is controlled in accordance with the current flow in said resonant circuit.

A further object of the present invention is to provide such a spark checking arrangement in which the inductance and capacitance elements of the resonant circuit are located in the electrode member itself.

' A further object of the present invention is to provide such a spark checking arrangement in which temperature responsive means is employed to actuate a switch in the burner circuit, which temperature responsive means is subjected to the heating effect of the current in the resonant circuit.

Other objects of the invention will be apparent from a considtration of the accompanying specification, claims and drawing, of which:

Figure 1 is a schematic view of a burner control system embodying one species of my invention;

Figure 2 is a detail view in section of one of the electrodes employed in the spark checking arrangement of the invention;

, Figure3 is a schematic view of a portion of an oil burner control system embodying a second species of the invention, and s Figure 4 is a view of the electrode and associated switch of the second species.

Referring to the drawing, more particularly to Figure 1 thereof, an oil burner is generally designated by the reference numeral III. This oil burner is of conventional construction and comprises a burner motor ii and a nozzle [2 through which a mixture of fuel and air is forced.

A room thermostat I5 is employed as a primary control of the oil burner. This room thermostat is of conventional construction being shown as K comprising a bimetallic element It to which is secured a contact arm i'l adapted to engage with a contact l8 upon the temperature falling below a predetermined point.

The thermostat l5 controls the energization of .a relay 20. This relay comprises a relay coil 2| and a pair of switch arms 22 and 22 adapted to be moved into engagement with contacts 24 and 25, respectively. Switch arms 22 and 22 are biased out of engagement with contacts 24 and 25 by any suitable means (not shown) and are adapted to be moved into engagement therewith upon energization of relay coil 21.

A thermal safety switch is generally designated by the reference character 21. This switch may be of any suitable form, one preferred form being that shown in the patent to Frederick S. Denison No. 1,958,081, issued May 8, 1934. As shown in the drawing, this switch comprises a pair of switch blades 28 and 29 the lower one 29 of which is pivotally mounted so that unless restrained it will drop away from switch blade 28. Normally projecting under the lower end of switch blade 29 to hold it in engagement with switch blade 29 is a bimetallic element 30. This bimetallic element has associated therewith a heater 3| which upon energization thereof is adapted to heat the bimetallic element 99 and warp it to the right. If this heating continues sufllciently far, the bimetallic element 90 will move from under the end of switch blade 29 allowing the latter member to drop away from switch blade 29.

A stack switch is generally indicated by the reference numeral 29. This switch is shown in a purely schematic form in the As shown, the switch. comprises two switch blades and 3?. Switch blade it is movable between contacts 38 and 39 and switch blade is prov-=- able between contacts to and The switch blades 3i are adapted to be actuated by a temperature responsive element (not shown), which element is placed so as to be responsive to stack temperature. The switch blades 38 and are connected to the temperature responsive element by a slip friction connection allowing the blades and to be moved. iron one contact position to their other contact position upon an initial temperature change he either direction, after which the temperature responsive element continues to move without movement of the switch blades by reason of the slip friction connection. This construction is well known in the art and is for the purpose of quickly responding to a change in direction of a temperature change.

The assembly consisting of the switch blade 35 and the contacts 38 and 39 is so designed that upon switch blade 35 moving to the right, as ocours with a temperature rise, the switch blade 35 engages contact 39 before it leaves contact 38. Upon a temperature fall, or in other words, upon switch blade 38 moving to the left, the switch blade does not engage contact 38 until it has disengaged contact 39. Thus the switch assembly is overlapping on temperature rise but nonoverlapping on temperature fall. Such an arrangement is shown in the patent to F. S. Denison et al., 1,941,540 of January 2, 1934. The switch blade 31 is overlapping on temperature rise, that is, upon moving to the right it engages contact 4| before it disengages contact 40. It is immaterial as to the sequence of contact en;- gagement when the switch blade 31 is moving in the reverse direction. Ordinarily, because of the greater simplicity of such a construction, the switch blade 31 would be overlapping in both directions.

Power for the system is supplied by two line wires 43 and 44. These line wires lead to any suitable source of power (not shown).

Located adjacent to the oil burner nozzle I2 are two electrodes 50 and 5I. These two electrodes are shown merely in schematic form in Figure l, the electrode 50 being shown in more detail in Figure 2. As indicated in Figure 1, a step-up transformer 53 is employed for supplying high voltage power for the energization of the circuit including the electrodes 58 and 5I. This transformer comprises a line voltage primary 5-1 and a high voltage secondary 55, to one terminal of which electrode 5I is connected by a conductor 85.

Referring now to Figure 2, the structure of the ignition electrode 58 is shown in greater detail. This electrode comprises an electrode tip 55 forming the electrode proper. This tip 56 is secured to a cylindrical shell 5'? of insulating material of suitable heat resistant properties. Located within the insulating shell 57 is an inductance coil 58, whose coil is electrically connected by a conductor 55 at one end to the electrode tip 55 and by a conductor at its other end to an insulated conductor forming one of the leads of the ignition circuit. Surrounding the insulating shell 5? and electrically connected to conductors and Cl is an elongated metal cupshaped member Surrounding member 53 an insulating sleeve and surrounding this sleeve is a second elongated metallic cup-shaped member 65. The two cup-she. ed members 53 and 85 which are separated by the insulating sleeve 64 constitute a condenser indicated schematically in Figure l and represented there by the reference numeral 68. As previously stated, the inner member 63 is connected to conductors 60 and 5!. The outer member 65 is connected by a conductor 6? to a resistance wire 69 having a relatively high temperature co-efficient of expansion. Wire 69 is in turn connected to conductor 59 leading to the electrode 58. The wire 59 is slidably supported in suitable supports 73 and H of insulating material and secured to the opposite ends of wire 55 is a member T of resilient material which by reason of the fact that it is of greater length than wire 63 is maintained in a bowed condition. Secured to the resilient member 10 is a contact II which is adapted to engage a fixed contact member shown only schematically in the drawing and indicated by the reference numeral I2.

As can be readily ascertained from the schematic showing of Figure 1, the assembly of the electrode unit 50 includes an inductance 58 and the condenser 66 connected in parallel, the condenser having the wire 59 in series therewith. Both the inductance and condenser, while connected in parallel with each other, are connected in series in the ignition circuit. The value of condenser 66 is so chosen with respect to inductance 58 that the condenser and inductance are in parallel resonance with each other at the high frequency of the current accompanying the discharge between electrodes 50 and SI. Due to the inherent distributed capacity in the ignition circult, there is inevitably an oscillatory discharge across the spark gaps of relatively high frequency. It is this high frequency at which the condenser 66 and inductance 58 are resonant.

Operation of species of Figures 1 and 2 The various elements of the system are shown in the relative positions which they occupy when the temperature in the space heated by burner I0 is at or above the desired value. Let it be assumed now that the temperature begins to fall so that contact arm ll of the thermostat I is moved into engagement with contact I8. When this occurs, the following circuit will be established to relay coil 20: from line wire 43, through conductor I5, bimetallic element I6, contact arm I1, contact I8, conductor IE, switch blades 28 and 29, conductor I1, switch blade 38, contact 38, conductor 18, heating element 3|, conductor I9, relay coil 28, and conductor 88 to the other line wire 44. The establishment of this circuit causes the energization of relay coil 28 with the result that switch blades 22 and 23 are moved into engagement with contacts 24 and 25.

The movement of switch blade 23 into engagement with contact 25 results in the establishment of the following circuit to the primary 54 of the ignition transformer 53: from line wire 43 through conductor 8 I, contact 25, switch blade 23, conductor 82, switch blade 31, contact 48, conductor 83, primary winding 54, and conductor 84 to the other line wire 44. The energization of primary 54 results in the energization of the ignition circuit so that normally a spark is produced between electrodes 58 and EI. If aproper spark occurs, the current will consist primarily of two components, one a low frequency component, the frequency of which is the same as the frequency of the supply source. The other component will be a high frequency one, the frequency of which is determined by the constants of the circuit.

' loop constitutes in effect a series resonant circuit for the current of that frequency and thus provides an impedance which, except for the resistance 69, is relatively negligible. The high frequency current by reason of its relatively large value will cause wire 69 to become heated. This in turn will cause the wire to expand permitting the bowed member 19 to move towards a more straightened position. This movement of member 19 brings the contact 1| into engagement with the fixed contact 12. Upon this happening, the following circuit is established to the oil burner motor 2 from line wire 49 through conductor 8|, contact 26, switch blade 29, conductor 81, contacts 12 and 1|, conductors 88 and 89, burner motor I, and conductor 99 to the other line wire 44. The establishment of this burner motor circuit results in fuel being ejected through the nozzle l2, which fuel by reason of the existence of a proper spark between the electrodes 69 and 5| is immediately ignited.

The ignition of the burner will result almost immediately in a rise in the stack temperature causing the switch blades 96 and 91 to be moved to the right. The movement of switch blade 96 to the right causes first the engagement thereof with contact 99 and then the disengagement thereof from contact 98. Upon the switch blade 96 engaging the contact 99, the following holding circuit is established to the relay 29: from line wire 49 through conductor 16, bimetallic element It, contact arm I1, contact l8, conductor 16. switch blades 28 and 29, conductor 11, switch blade 96, contact 99, conductor 9|, switch blade 22, contact 24, conductor 92, relay coil 29 and conductor 89 to the other line wire 44. It will be noted that this new circuit is independent of the heating element 9|. switch blade 96 from contact 98 causes the interruption of the previously traced circuit to the heating element 9|. By reason of the overlapping action, the new circuit is established before the interruption of the old circuit so that there is no interruption in burner operation. The interruption of the circuit to heating element 9| causes this element to no longer be raised in temperature so that it is assured that the burner motor will remain in operation.

The movement of switch blade 91 into engagement with contact 4| results in the-establishment of the following new circuit to oil burner motor II: from line wire 49 through conductor 8|, contact 26, switch blade 29, conductor 82,- switch blade 91, contact 4|, conductors 89 and 88, burner motor II, and conductor 89 to 'the other line wire 44. It will .be noted that this new circuit is independent of contacts 1| and 12. The disengagement of switch blade 91 from'contact 49 results in the interruption of the PM! ously traced ignition circuit. The ignition is thus deenergized, being no longer needed since the oil burner is now in operation. If it were not for the establishment of the last traced oil burner circuit, separation of contacts 1| and 12 by reason of the deenergization of the ignition apparatus would stop the oil burner. By reason, however, of the new circuit which in eflect parallels the contacts 1| and 12, the oil burner motor continues in operation.

The disengagement of The operation which has just been described is that which occurs when combustion takes place in the ordinary manner. If the oil burner is never started by reason of a proper spark not being established or if for some other reason combustion is not established, the circuit to heating element 9| will not be interrupted. The result is thatafter a predetermined period of time, the bimetallic element 99 is warped sufficiently to the right to permit separation of switch blades 28 and 29. Such separation will interrupt all of the circuits to relay coil 29 and completely deenergize the system. The system will not again be placed into operation until the switch blades 28 and 29 are again reclosed manually. This necessity for a manual resetting of the switch blades 28 and 29 insures that the operator will have a chance to determine the cause of the failure of combustion.

If at any time after combustion has been established it is interrupted for some reason or other, the stack temperature will again cool causing stack switch blades 96 and 91 to be moved to the left. The movement of switch blade 96 out of engagement with switch blade 99 causesthe deenergization of the holding circuit for relay coil 29. Since the switch blade 96 does not engage contact 98 until some time after it is separated from contact 99, there will be a period during which there is no energizing circuit for relay coil 29. During this period, the oil burner is out of operation permitting any accumulation of vaporized oil which may be present to escape up the stack. On switch blade 96 reengaging the contact 98, relay coil 29 will again be reenergized by reason of the establishment of the first traced energizing circuit therefor. The movement of switch blade 91 to the left into engagement with upon recycling after flame failure, the present arrangement offers a relatively simple method of insuring that the oil burner is not placed in operation until there is a proper spark. It will further be noted that the apparatus will not falsely respond to a spark occurring somewhere between the ignition leads. This is ,a very serious problem inasmuch as the ignition circuits I are usuallyof quite high voltage. In spite of efforts to insulate the conductors between the ignition transformer and the spark electrodes, breakdown often does occur. In certain prior arrangements, it has been proposed to employ various devices, some responsive to high frequency potentials, which are solely responsive to the potential existing across the two leads. The disadvantage of such devices is that they respond in case of any breakdown between the ignition leads due to the fact that in spite of the breakdown a high frequency voltage exists between these leads even though there be no spark in the spark gap whatsoever. The present arrangement by reason of the fact that it is connected closely adjacent the ignition electrode and in series therewith prevents any such false indication of tam-ah.

a proper spark by reason of a spark between the ignition leads.

Species of Figures 3 and 4 In Figures 3 and 4, a slightly different form of the invention is shown. Inasmuch as the oil burner circuit is substantially the same as in the species of Figures 1 and 2, only a portion of the oil burner circuit has been shown. In view of the fact that the oil burner is identical, it has been given the same reference characters as in Figure 1, the oil burner motor being designated by the reference numeral II and the nozzle by the numeral I2. The ignition electrodes in this species are designated by the reference numerals IN and I02, respectively. The electrode I02, like the electrode of the previously described species, consists of an assembly of several elements. The electrode I02 comprises an electrode tip I03 constituting the electrode proper. This tip I03 is secured to a shell I04 of insulating material of suitable heat resistant properties. Located within the insulating shell I04 is an inductance coil I05 which has a central passage therethrough. The inductance coil I05 is so designed that its distributed capacity makes the coil I05 resonant at frequencies accompanying a proper spark in the ignition circuit. One end of the inductance coil I05 is connected by a conductor I06 to the electrode tip I03. Located within the passage of coil I05 is a bulb I01 which is connected to a metallic tube I08. Tube I08 is connected at its outer extremity to a bellows I09 which bears against a pivoted support member III) for a mercury switch III. The mercury switch III is of conventional structure comprising a pair of contacts I I3 and I I4 which are adapted to be bridged by a mercury element H5. A spring IIZ biases the support H0 to a position wherein the mercury II5 is out of engagement with contacts II 3 and H4. The left-hand end of the coil I05 is connected by a conductor H6 to the metal tube I08, which in turn is connected to a conductor H1 which leads to one terminal of the ignition transformer.

The bulb I01 is of relatively high conductivity so as to form a short circuited secondary for the inductance coil I05. It will be readily seen that when a high frequency current flows through the inductance I05, the currents introduced in the metallic bulb member I01 will be of sufllciently great intensity as to heat the bulb I01. Due to the resonant nature of the coil I05, these currents will flow only when a proper spark occurs between the electrodes. Located within the bulb I01 is a mixture I20 consisting of gas and activated charcoal. Under normal conditions, the gas will largely be absorbed by the activated charcoal. As the temperature of the bulb I01 rises, however, gas will be forced out of the activated charcoal expanding the bellows I09 and causing the mercury switch I I I to be tilted to its closed position wherein contacts H3 and H4 are bridged by mercury switch II5. It is to be understcod that in lieu of the gas and activated charcoal fill, there may be substituted a fill of a suitable volatile fluid which is adapted to operate within the temperature range to which it will be switch III are connected in the same manner as the contacts II and 12 of the previously described species. These contacts perform the same function as contacts 1| and 12 of the other species.

It will be seen that in both modifications of my invention a very reliable checking of the spark is obtained with a relatively simple structure which occupies very little additional space, while in both species, the various disadvantages outlined for the prior art are successfully avoided without any accompanying disadvantages of their own.

While certain specific embodiments of the invention have been shown, it is to be understood that these are for purposes of illustration only and that the invention is to be limited only by the scope of the appended claims.

I claim as my invention:

1. In combination, a burner, means controlling the flow of fuel to said burner, an ignition circuit including a pair of spaced electrodes for igniting the fuel supplied by said fuel flow controlling means, one of said electrodes having a hollow portion, temperature responsive means within said hollow portion, means associated with said electrode to heat said temperature responsive means upon the occurrence of a proper spark between said electrodes, a control device actuated by said temperature responsive means, and means including said control device operative to so control the fuel flow controlling means as to cause a flow of fuel to said burner only when there is a proper spark between said electrodes.

2. In combination, a burner, means controlling the flow of fuel to said burner, an ignition circuit including a pair of spaced electrodes for igniting the fuel supplied by said fuel flow controlling means, one of said electrodes having a hollow portion, a fluid filled member within said hollow portion, means associated with said electrode to heat said member upon the occurrence of a proper fluid pressure actuated means connected to said fluid filled member and operatively connected to said control device to move the same to either of two controlling positions, and means including said control device operative to so control the fuel flow controlling means as to cause a flow of fuel to said burner only when there is a proper spark between said electrodes.

3. In combination, a burner, electrically operated means controlling the flow of fuel to said burner, an ignition circuit including a pair of spaced electrodes for igniting the fuel supplied by said fuel flow controlling means, one of said electrodes having a hollow portion, temperature responsive means in said hollow portion, means associated with said electrode to heat said temperature responsive means upon the occurrence of a proper spark between said electrodes, a switch associated with said electrode and operatively connected to said temperature responsive means to be actuated thereby, and means including said temperature responsive means and said switch operative to so control the fuel flow controlling means as to cause a fiow of fuel to said burner only when there is a proper spark between said electrodes.

4. In combination, a burner, electrically operated means controlling the flow of fuel to'said burner, an ignition circuit including a pair of spaced electrodes for igniting the fuel supplied by said fuel flow controlling means, one of said electrodes having a hollow portion, a'fluid filled member in said hollow portion, means associated with said electrode to heat said temperature rev trode and operatively associated with said switch sponsive means upon the occurrence of a'proper spark between said electrodes, a switch, fluid pressure responsive means connected to said fluid fuel member and operatively connected to said switch for actuating the same, and means including said switch operative to so control the fluid fuel controlling means as to cause a flow of fuel to said burner only when there is a proper spark between said electrodes.

5. In combination, a burner, electrically operated means controlling the flow of fuel to said burner, an ignition circuit including a pair of spaced electrodes for igniting the fuel supplied by said fuel flow controlling means and having suflicient capacity that the occurrence of a proper spark between said electrodes causes the flow of a high frequency current in said ignition circuit, one of said electrodes having a hollow portion including inductance and capacitive means connected in parallel with each other and in series with the remainder of the electrode and a switch actuating means associated with said inductance and capacitive means, a switch associated with said electrode and operatively associated with said switch actuating means, and means including said switch operative to so control the fuel flow controlling means as to cause a flow of fuel to said burner only when there is a high frequency current flow in said ignition circuit.

6. In combination, a burner, electrically operated means controlling the flow of fuel to said burner, an ignition circuit including a pair of spaced electrodes for igniting the fuel supplied by said fuel flow controlling means and having sufficient capacity that the occurrence of a proper spark between said electrodes causes the flow of a high frequency current in said ignition circuit, one of said electrodes having a hollow portion including inductance and capacitive means connected in parallel with each other and in series with the remainder of the electrode, a switch actuating means including a heating device located in said electrode and connected in series with said capacitive means, a switch associated with said elecactuating means, and means including said switch operative to so control the fuel flow controlling means as to cause 'a flow of fuel to said bumer only when there is a high frequency current flow in said ignition circuit.

7. In combination, a burner, electrically operated means controlling the flow of fuel to said burner, an ignition circuit including a pair of spaced electrodes fcr igniting the fuel supplied by said fuel flow controlling means and having sufflcient capacity that the occurrence of a proper spark between said electrodes causes the flow of a, high frequency current in said ignition circuit, one of said electrodes having a hollow portion including inductance and capacitive means connected in parallel with each other and in series with the remainder of the electrode, a switch associated with said electrode, fluid pressure responsive means for actuating said .switch, a fluid filled metallic receptacle connected to said pressure responsive means and located in inductive relationship with said inductance whereby upon the flow of high frequency current in said inductance said metallic receptacle is heated by reason of the cur ent flow induced therein, and means including said switch operative to so control the fuel flow controlling means as to cause a flow of fuel to said burner only when said receptacle is heated.

8. Incombination, a burner, electrically operated means controlling the flow of fuel to said burner, an ignition circuit including a pair of spaced electrodes for igniting the fuel supplied by said fuel flow controlling means and having sufflcient capacity that the occurrence of a proper spark between said electrodes causes the flow of a high frequencycurrent in said ignition circuit, one of said electrodes having a hollow portion, an inductance element in said hollow portion, a metallic shell surrounding said inductance element, a second metallic shell surrounding said previously named shell and insulated therefrom, said shells collectively acting as a condenser and as a casing for said hollow portion, a switch ac- .tuating means associated with said inductance elementv and said condenser, a switch associated with said electrode and operatively associated with said switch actuating means, and means includingsaid switch op rative to so control the fuel flow controlling means as to cause a flow of fuel to .said burner only when there is a high frequency current flow in said ignition circuit.

MEADE J. MAYNARD.

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