US3609072A

US3609072A - Electric igniter system

Info

Publication number: US3609072A
Application number: US845954A
Authority: US
Inventors: James R Willson
Original assignee: Robertshaw Controls Co
Current assignee: Robertshaw Controls Co
Priority date: 1969-07-30
Filing date: 1969-07-30
Publication date: 1971-09-28
Anticipated expiration: 1988-09-28

Abstract

An electric igniter system for a fuel burner including an electrical resistance type igniter, wherein the resistance element is of a type having a negative temperature coefficient and is coupled to a thermistor having a positive temperature coefficient. An electrically operated fuel valve is energized only after the igniter and thermistor resistances have been changed by heat from the igniter to values corresponding to the generation of fuel ignition temperatures by the igniter.

Description

United States Patent [72] Inventor James R. Willson Garden Grove, Calif. [2]] Appl. No. 845,954 [22] Filed July 30, 1969 [45] Patented Sept. 28, 1971 73] Assignee Robertshaw Controls Company Richmond, Va.

[54] ELECTRIC lGNlTER SYSTEM 13 Clalms, 4 Drawing Figs.

|52| US. Cl 431/66, 317/98, 431/254 [5 I Int. Cl F23n 5/14 [50] Field of Search 431/66, 24, 6, 254; 317/98, 79; 123/32 [56] References Cited UNITED STATES PATENTS 2,316,910 4/1943 Weber 431/66 X 2,549,633 4/1951 Ottmar 431/66 X 2,621,647 12/1952 Pace 431/66 X 3,151,661 10/1964 Matthews.. 431/66 X 3,282,324 11/1966 Romanelli. 431/24 3,454,345 7/1969 Dyre 431/66 Primary Examiner-Frederick L. Matteson Assistant ExaminerRobert A. Dua

Attorneys-Auzville Jackson, Jr., Robert L, Marben and Anthony A. OBrien IBURNER! :JLFUEL VALVE -FUEL INPUT 26 ATENIfinsePzsmam :2 609 ,072

I 26 BURNER 5x56 -FUEL INPUT INVENTOR JAMES R. WILLSON ATTORNEY ELECTRIC rcurrsa SYSTEM BACKGROUND OF THE INVENTION l. Field of the Invention The present invention relates to electric igniter systems for fuel burners and, more particularly, to an igniter system wherein an electric igniter element having a negative temperature coefficient of resistance is utilized in conjunction with a thermistor having a positive temperature coefficient to provide fail-safe operation.

2. Description of the Prior Art Devices such as the bimetallic element have been employed quite satisfactorily as heat sensors in systems employing pilot flame igniters to prevent raw fuel leakage into the area surrounding the system burner upon pilot flame outage. However, certain drawbacks soon become apparent; for example, pilot flame outage due to dust particle buildup was found to be common, and the slow switching time of the bimetallic sensors often caused raw fuel leakage thereby creating a potentially dangerous condition.

Electric igniter systems have proven to be both reliable and efficient and have the ability to operate under the control of rapid acting electrical safety circuits, thereby eliminating a substantial hazard. In some instances, practical electric igniter elements having negative temperature coefficients of resistance have been utilized for ignition and control of fuel flow. While such igniter systems have particular advantages in their respective arrangements, it is desirable to develop igniter systems having increased safety, simplicity of operation and economy of manufacture.

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to construct an electric ignition system having all the advantages of similarly employed prior art systems but utilizing fewer components than the components essential to such systems.

Another object of this invention is to provide an electric igniter system employing an igniter element having a negative temperature coefficient of resistance as both an igniting means and a heat sensing means.

This invention has a further object in the provision of an electric ignition system having fail-safe characteristics assuring fuel ignition.

An additional object of the present invention is the provision of an electric ignition system having raw fuel leakage prevention characteristics in the event of either an open circuit or a short circuit in the igniter element.

An advantage of the invention is the provision of a simple and reliable electric igniter system having few parts and inherent safety characteristics.

The present invention is summarized in that an electric ignition system for a fuel burner includes an electrical power source coupled to an electric igniter having a negative temperature coefficient of resistance which is adapted to be located within igniting proximity of the burner. The system further includes a resistor adapted to be heated by the igniter and having a positive temperature coefiicient, and an electrically operated valve adapted to control a flow of fuel to the burner. The igniter, resistor and valveare coupled to a circuit which is responsive to the resistance of the igniter and the resistor for enabling energization of the valve,v to thereby establish a flow of fuel, only when the igniter is above fuel igniting temperatures and for disabling the valve when the igniter develops either an electrical short circuit or an electrical open circuit.

These and other objects and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiments of the invention when considered in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic circuit diagram of an electric igniter system embodying the present invention;

FIG. 4 is a schematic circuit the circuit illustrated in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS diagram of a modification of FIG. 1, which illustrates a preferred embodiment of the present invention, includes an electric igniter 10 having a negative temperature coefficient of resistance, connected in series with a positive temperature coefficient resistor 12 and a switch 14. The entire series circuit is connected to a source of electrical power, illustrated for simplicity by lines 16. The energization winding 18 of an electromagnetic relay 20 is connected in parallel with resistor 12 while the normally open relay contacts 22, which are mechanically biased to an open position (as illustrated) in the absence of electrical energization of the winding 18, are coupled in series with an electrically operated fuel valve 24. The series circuit formed by switch 22 and valve 24 is coupled in parallel with igniter 10 to complete the electrical circuit.

Fuel valve 24 is mechanically coupled in the fuel line 26 so as to control the flow of fuel from the fuel source to the burner 28 that is suitably supported in conventional burner apparatus 30. The igniter 10 is located within igniting proximity of the burner 28 while resistor 12 is adapted to be positioned ad- 30 jacent the igniter so that the temperatures of the igniter and the resistor are maintained approximately equal. It is noted that while the physical location of igniter 10, resistor 12 and burner 28, with respect to each other, is the same for all embodiments of the present invention, it has been schematically illustrated only in FIG. I for the sake of simplicity and clarity, it being understood that a similar placement of the elements in all the figures is intended.

Referring now to FIG. 2, igniter 10 is connected in series with resistor 12 and switch 14 across power source 16, as in FIG. 1. However, in this embodiment relay energization winding 18 is connected in parallel with igniter 10 while fuel valve 24 is connected in parallel with resistor 12 via relay contacts 22.

In FIG. 3, the same basic circuit is shown as in FIG. I with the exception that the relay energization winding is connected in series with the then'nistor l2 and is constructed so as to be current sensitive rather than being voltage sensitive as in the preceding two figures.

FIG. 4 is a modification of the circuit of FIG. 3 with the substitution of a bimetal actuated switching device 40 for relay 20. Device 40 includes a switch 42 which is directly controlled by the movement of a bimetallic arm 44 mounted upon a frame 46. Bimetallic arm 44 is illustrated in its cold position wherein switch 42 is maintained closed. The arm 44 is heated by a heating element 48 which is connected in parallel with igniter 10 through one side of a single pole double throw switch 50. Switch 50 is controlled through a snap-action spring 52 by lever arm 54 which is pivotally mounted upon frame 46 and is biased by spring 56 against the free end of bimetallic arm 44. Thus, in the position shown, switch 50 provides a closed path from the igniter to the heater element 48 through the lower contacts, as shown. The upper contacts of switch 50 complete the parallel connection of fuel valve 24 to the igniter 10 for energization. The device 40 also includes a holding coil 58 which functions to hold lever arm 54 after it has been moved downward by bimetallic arm 44 but is incapable of generating a sufficient magnetic field to pull lever 54 down from its unactuated position, as illustrated.

In explaining the operation of the circuits described above. a typical installation of the igniter circuit in a central heating furnace system will be used. In such a system, switch l4 would function in a conventional manner either as a main power switch, a thermostatically operated ambient temperature sensing device, or a combination power thermostat switch. It

should also be noted that the placement of switch 14 in the circuit is not critical to the invention and may be modified in accordance with the particular operational characteristics desired for various different installations.

Referring to FIG. 1, when the circuit is

inactive switches

14 and 22 will be open, as shown. Since no power will therefore be applied, the temperature of both the igniter and the thermistor 12 will be low; and, due to the negative and positive temperature coefficients of resistance of the igniter and thermistor, respectively, the initial resistance of the igniter will be high in comparison with that of the thermistor.

When a demand for heat arises, switch 14 will become closed to thereby feed power from the source 16 to the series combination of thermistor l2 and igniter 10. By visualizing this series circuit as a resistive voltage divider, the initial voltage drop across the igniter 10 can be seen to be high with respect to the thermistor I2 in direct relation to the initial value of their respective resistances. At this same time, the igniter begins to increase in temperature which causes the voltage drop of the igniter to decrease and that of the thermistor to increase as their resistances vary. Thus, the voltages appearing across the two major heat sensing components, namely thennistor l2 and igniter l0, vary in opposite directions in proportion to the temperature of the igniter 10.

In the circuit of FIG. I, the voltage drop across the thermistor is applied to relay energiz'ation winding 18, while the drop across the igniter is fed tothe fuel valve 24 via the relay contacts 22. Therefore, prior to igniter heat-up the small voltage across the thermistor 12 will be insufficient to energize the relay and the large voltage drop across the igniter will be prevented from actuating the fuel valve by the open switch contacts 22. In this embodiment, the relay 20 is voltage sensitive and will close contacts 22 only after the resistance of the thennistor, and therefore its voltage drop has been increased by the heating of the igniter to fuel igniting temperatures. As a result, initial fuel flow is prevented until sufficient igniter temperature has been attained, thus assuring immediate ignition whenever fuel if fed to the burner.

Considering now the operation of the circuit after burner ignition has been established,.it is noted that the igniter 10 is coupled in series with the parallel combination of thermistor I2 and energization winding I8, and is coupled in parallel with the series combination of fuel valve 24 and relay contacts 22. Therefore, if the igniter devclopes an open circuit, the flow of current through the thermistor-relay parallel circuit will cease causing immediate drop out of contacts-22 to thereby stop the flow of fuel. In the event of a short circuit in the igniter, the voltage across the fuel valve 24 will drop to zero causing its immediate closure. Thus, both open and short circuit protection is provided to assure failsafe operation at all times.

The circuit of FIG. 2 operates in similar manner as that of FIG. 1. In this Figure, however, the relay winding is connected in parallel with the igniter while the fuel valve is connected across the thermistor through the relay switch 22. In operation, the initial large voltage drop across the igniter upon closure of switch 14 in response to a demand for heat energizes relay 20 to place the fuel valve directly across thermistor 12. However, the fuel valve in this embodiment is voltage sensitive and will not function to establish a flow of fuel to the burner until the resistance of the thermistor, and therefore, its voltage drop has been increased by the heating of the igniter to fuel igniting temperatures. Therefore, raw fuel leakage is prevented during periods of normal operation.

As in the circuit of FIG. I, igniter short circuit and open cir cuit protection is provided by the system of FIG. 2. More specifically, the series connection of the fuel valve and the igniter is designed to block the flow of current to the fuel valve if, for any reason, the igniter becomes an open circuit. This inherently causes the fuel valve to shut off the fuel flow to the system burner to prevent raw fuel from collecting. A short cir cuit in the ignition element will also produce immediate fuel cutoff since the short circuit will remove the energization voltage from the relay winding 18 causing the relay contacts 22 to rent is drawn by the combination. The relay, thermistor and igniter are designed to provide the requisite current flow only after the igniter has reached fuel igniting temperatures to thereby prevent raw fuel leakagelt is noted that in this embodiment the rate of change of resistance is greater for the igniter than for the thermistor so that the net rate of change of current flowing therethrough increases as the temperature of the igniter increases, the thermistor functioning to limit the current through the circuit to prevent thermal runaway by the igniter.

In the event that the igniter becomes an open circuit, the current flow through the relay winding will cease and fuel flow will be blocked by the fuel valve 24. Similarly, if the igniter becomes a short circuit, the energization voltage across the fuel valve will become zero, thereby causing immediate closure thereof.

Referring now to FIG. 4, when switch I4 is initially closed, current will flow through the igniter 10, the thermistor l2 and the holding coil 58. The initial voltage drop is primarily across the igniter since thermistor 12 has an initial low resistance and holding coil 58 is selected to be of a low impedance current sensing type. The large potential drop across the igniter is fed to heater element 48 through the lower set of contacts of switch 50 whereupon the heat generated thereby causes bimetallic arm 44 to deflect away from the heater 48. This causes switch 42 to open and then, by movement of lever arm 54, causes switch 50 to snap to its upper position whereupon the heater element 48 is removed from the circuit. During this series of events the igniter 10 becomes hot thereby changing its resistance to permit a larger flow of current through the holding coil 58.. The coil then produces sufficient magnetization to maintain lever arm 54 in its deflected position, thereby maintaining the upper contacts of switch 50 closed, while bimetallic arm 44 begins to return to its cold or rest position. The bimetal, as it continues to return to rest, then closes switch 42 to complete the parallel connection of the fuel valve with the igniter through switch 42 and the upper contacts of switch 50. The system is designed so that the aforedescribed series of events will occur in no shorter time than the time required for igniter 10 to come up to fuel ignition temperatures. This safety factor is further increased by the fact that only after the resistance of igniter 10 has been decreased by the generation thereby of fuel ignition temperatures will sufficient current flow through the holding coil 58 to maintain lever arm 54 and, therefore, switch 50 in their actuated positions. 1

After ignition, if the igniter in the'circuit of FIG. 4 develops a short circuit, the voltage across the fuel valve will become zero thereby cutting ofi the flow of fuel to the burner. Similarly, the voltage to the fuel valve will be removed by the switch 50 if the igniter develops an open circuit since the current flow through the holding coil will cease and lever arm 54 will be released.

Therefore, there is provided in all of the illustrated embodiments an electric igniter system which is permitted to cycle continuously in response to a demand for heat while providing raw fuel leakage prevention as well as igniter short or open circuit fail-safe operation.

In as much as the present invention is subject to many variations, modifications and changes in detail, it is intended that all matter contained in the foregoing description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

. What is claimed is:

I. An electric ignition system for a fuel burner comprising input means adapted to be connected with an electrical power source,

an electric ignitor coupled to said input means and adapted to be located within igniting proximity of the burner,

said igniter having a negative temperature coefficient of resistance,

a resistor having a positive temperature coefficient of resistance coupled in series with said igniter and adapted to be heated thereby,

an electrically operated valve adapted to control a flow of fuel to the burner, and

means coupled to said ignitor, said resistor, and said valve and responsive to the relative resistances of said ignitor and said resistor for enabling energization of said valve to establish a flow of fuel when said ignitor is above fuel igniting temperatures and for disabling said valve upon failure of said ignitor.

2. The invention as recited in claim 1 wherein said means includes an electric relay having an energization winding and a switch responsive thereto, said switchbeing coupled in series with said valve to form a series circuit.

3. The invention as recited in claim 2 wherein said series circuit is coupled in parallel with said resistor, and said energization winding is coupled in parallel with said ignitor.

4. The invention as recited in claim 2 wherein said series circuit is coupled in parallel with said igniter and said energization winding is coupled in parallel with said resistor.

5. The invention as recited in claim 2 wherein said series circuit is coupled in parallel with said igniter and said energization winding is coupled in series with said resistor and said ignitor.

6. The invention as recited in claim 5 further including thermally responsive switch means connected with said valve and said relay, said thermally responsive switch means including a bimetallic element and an electric heater located within heating proximity of said bimetallic element and coupled with said ignitor.

7. The invention as recited in claim 6 wherein said thermally responsive switch means further includes a normally closed switch coupled in series with said valve and said relay switch and adapted to be opened by said bimetallic element in response to energization of said electric heater, and wherein said relay further includes a normally closed switch connected in series with said electric heater, said relay being initially actuated by said bimetallic element and being maintained in its actuated position by said energization winding whenever said ignitor is above fuel igniting temperature.

8. In an electric ignition system for a fuel burner, the combination comprising input means adapted to be connected to an electrical power source,

an electric ignitor adapted to be located adjacent the burner and coupled to said input means,

said ignitor having a negative temperature coefficient of resistance thereby producing a temperature dependent voltage drop thereacross, an electrically operated valve adapted to control a flow of fuel to the burner and being electrically coupled with said electric ignitor and said input means for energization by said power source when said ignitor is above fuel ignition temperature, switch means connecting said electrically operated valve with said ignitor whereby said valve is deenergized to thereby inhibit fuel flow therethrough whenever said ignitor develops an electrical short circuit, and circuit means connected with said ignitor and said switch means for disabling said valve to thereby inhibit fuel flow therethrough when said ignitor develops an electrical open circuit. 9. The invention as recited in claim 8 wherein saidswitch means connects said electrically operated valve across said igniter and wherein said circuit means is connected in series circuit with said ignitor said switch means and said circuit means cooperating to inhibit actuation of said valve until said ignitor reaches fuel ignition temperatures.

10. The invention as recited in claim 9 wherein said circuit means comprises a resistor having a positive temperature coefficient of resistance and an energization winding of an electric relay coupled to form an electrical parallel circuit, and wherein said switch means comprises a normally open switch adapted to be closed in response to energization of said winding, said switch being coupled in series with said electrically operated valve.

11. The invention as recited in claim 9 wherein said circuit means comprises a resistor having a positive temperature coefficient of resistance and an energization winding of an electric relay coupled to form a series circuit, and wherein said switch means comprises a normally open switch adapted to be closed upon energization of said winding, said switch being coupled in series with said electrically operated valve.

12 The invention as recited in claim 11 wherein said energization winding is a holding coil, and wherein said switch means further includes thermally responsive switching means connected with said electrically operated valve and said normally open switch, said thermally responsive switch means including a bimetallic element and an electric heater located within heating proximity of said bimetallic element and coupled with said ignitor.

13. The invention as recited in claim 12 wherein said thermally responsive switching means further includes a normally closed switch coupled in series with said electrically operated valve and said normally open switch and adapted to be opened by said bimetallic element in response to energization of said electric heater, and wherein said relay further includes a normally closed switch connected in series with said electric heater, said relay being initially actuated by said bimetallic element and being maintained in its actuated position by said holding coil whenever said ignitor is above fuel igniting temperatures.

Claims

1. An electric ignition system for a fuel burner comprising input means adapted to be connected with an electrical power source, an electric ignitor coupled to said input means and adapted to be located within igniting proximity of the burner, said igniter having a negative temperature coefficient of resistance, a resistor having a positive temperature coefficient of resistance coupled in series with said igniter and adapted to be heated thereby, an electrically operated valve adapted to control a flow of fuel to the burner, and means coupled to said ignitor, said resistor, and said valve and responsive to the relative resistances of said ignitor and said resistor for enabling energization of said valve to establish a flow of fuel when said ignitor is above fuel igniting temperatures and for disabling said valve upon failure of said ignitor.

2. The invention as recited in claim 1 wherein said means includes an electric relay having an energization winding and a switch responsive thereto, said switch being coupled in series with said valve to form a series circuit.

8. In an electric ignition system for a fuel burner, the combination comprising input means adapted to be connected to an electrical power source, an electric ignitor adapted to be located adjacent the burner and coupled to said input means, said ignitor having a negative temperature coefficient of resistance thereby producing a temperature dependent voltage drop thereacross, an electrically operated valve adapted to control a flow of fuel to the burner and being electrically coupled with said electric ignitor and said input means for energization by said power source when said ignitor is above fuel ignition temperature, switch means connecting said electrically operated valve with said ignitor whereby said valve is deenergized to thereby inhibit fuel flow therethrough whenever said ignitor develops an electrical short circuit, and circuit means connected with said ignitor and said switch means for disabling said valve to thereby inhibit fuel flow therethrough when said ignitor develops an electrical open circuit.

9. The invention as recited in claim 8 wherein said switch means connects said electrically operated valve across said igniter and wherein said circuit means is connected in series circuit with said ignitor, said switch means and said circuit means cooperating to inhibit actuation of said valve until said ignitor reaches fuel ignition temperatures.

11. The invention as recited in claim 9 wherein said circuit means comprises a resistor having a positive temperature coefficient of resistance and an energization winding of an electric relay coupled to form a series circuit, and wherein said switch means comprises a normally open switch adapted to be closed upon energization of said winding, said switch being coupled in series with said electrically operated valve. 12 The invention as recited in claim 11 wherein said energization winding is a holding coil, and wherein said switch means further includes thermally responsive switching means connected with said electrically operated valve and said normally open switch, said thermally responsive switch means including a bimetallic element and an electric heater located within heating proximity of said bimetallic element and coupled with said ignitor.