US3551084A - Electric ignition system having a ptc ignitor element - Google Patents

Description

ELECTRIC IGNITION SYSTEM HAVING A FTC IGNITOR ELEMENT Filed March 14, 1969 z Sheets-Sheet 1 Lu 03 5 a) co Lu a0 0.2 ho OJ- 3- h no I) M Mvm' ATTORNEYS J. R. WILLSON Dec. 29, 1970 ELECTRIC IGNITION SYSTEM HAVING A PTC IGNITOR ELEMENT Filed March l4, 1969 2 Sheets-Sheet 2 QM ww bo 2 5&3 mm N l w ON "W.

9 NT wv W om mm ww vm mm R O n mm m H w W a m 1 a d on m wm m m P A o. I o m m o o w o o o o o 97 7 F a /i r m rum MQE ATTORNEYS United States Patent O 3,551,084 ELECTRIC IGNITION SYSTEM HAVING A PTC IGNITOR ELEMENT James R. Willson, 9342 Bixby Ave., Garden Grove, Calif. 92641 Filed Mar. 14, 1969, Ser. No. 807,183 Int. Cl. F23n 5/04 US. Cl. 43166 Claims ABSTRACT OF THE DISCLOSURE An electric ignition system for a fuelburner including an electrical resistance type ignitor, wherein the resistance element is of a type having a positive temperature coefficient and is connected in parallel with an electromagnetic holding coil and in series with a current-sensitive ballast device. The ballast device includes the parallel combination of a ballast resistor and the series circuit including a switch coupled to the holding coil and an electromagnet valve for controlling a flow of fuel to the fuel burner. The voltage drop of the circuit is primarily across the ballast device until the ignitor heats and thus increases in electrical resistance. The electromagnetic holding coil, being in parallel with the ignitor, senses the change in the voltage across the ignitor and permits energization of the fuel valve only after the ignitor has reached fuel igniting temperatures.

BACKGROUND OF THE INVENTION The present invention relates to electric ignition systems for fuel burners and, more particularly, to an improved electric ignition system utilizing an electric ignitor element having a positive temperature coefficient of resistance and having increased inherent safety characteristics.

Recent discoveries of various electric ignitor materials having desirable characteristics for commercial use have made electric ignition systems employing such devices increasingly important. One of the many basic goals sought after by engineers in this field is the provision of a circuit which is relatively simple, has few components, and will fail safe under abnormal conditions.

Typical of such devices are circuits which employ a heat sensing element to monitor the burner flame. The heat sensing element is very often either a thermistor to detect heat directly or a photoelectric light detector to sense the light emitted by the burner flame. The electric-a1 control circuitry associated with these elements, as well as the elements themselves, are quite complex and often operate with considerable lag time which, in certain circumstances, can create a dangerously explosive condition in the immediate burner area.

Different attempts to reach the aforementioned goal and to solve its associated problems have resulted in circuits which are only partially satisfactory due to either their complexity, their difficulty of production, or their lack of sufficient safety characteristics.

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 prior art systems.

Another object of this invention is to provide an electric ignition system with an electric ignitor element acting 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 increased fail-safe characteristics.

An additional object of the present invention is the pro- "ice vision of simplified control circuitry for use with an electric ignitor having a positive coefiicient of resistance.

A still further object of this invention is to construct an improved electric ignition system having increased safety characteristics for preventing raw fuel leakage.

The present invention is summarized in that an electric ignition system for a fuel burner includes an electrical power source and an electric ballast device. An electromagnet valve is coupled in parallel with the ballast device and is adapted to control a flow of fuel to the burner. An electric ignitor, adopted to be located adjacent to the burner and having a positive temperature coefficient of resistance, is electrically coupled to form a parallel network with an electromagentic relay which is energized by a voltage having at least a particular value. A set of normally-open contacts are coupled to the electromagnetic relay and are adopted to be closed when the relay is energized, the normally-open contacts being electrically coupled in series with the electric ballast device and the ignitor across the electrical power source for energization thereby. The parallel network of the electromagnetic relay and the electric ignitor has a voltage drop thereacross which is directly proportional to the temperature of said ignitor and has a value equal to the abovementioned particular value when the ignitor is above fuel igniting temperatures.

An advantage of the invention is the provision of a simple, reliable, and effective electric ignition system hav-- ing few parts and improved safety characteristics.

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

BRIEF DECRIPTION OF THE DRAWINGS FIG. 1 shows a schematic circuit diagram of an ignition system embodying the present invention, illustrating the position of the various components upon initial energization;

FIG. 2 shows a schematic circuit diagram of the circuit of FIG. 1 showing the position of the various components a brief time after energization; and

FIG. 3 shows a schematic circuit diagram of the circuit of FIG. 1 illustrating the position of the various components in their energized steady-state.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1, which illustrates the preferred embodiment of the invention, shows an electric ignitor 10, having a positive temperature coefiicient of resistance, connected in parallel with an electromagnetic holding coil 12. One side of the parallel combination is coupled to terminal 14 of the secondary winding of a transformer 16, having its primary winding coupled to an electrical power source, represented for simplicity by lines 18, via switch 20. The other terminal 22 of the secondary winding of transformer 16 is connected through the energization winding of an electromagnet fuel valve 24 to movable contact arm 26 of switching device 28. The electromagnet fuel valve 24 controls the flow of fuel from a fuel supply (not shown) via conduit 30 to the system fuel burner 32. Fuel valve 24 is shown in FIG. 1 in its closed position.

Switching device 28 includes stationary contact arms 34 and 36, connected to the contact of stationary arm 36 is a ballast heating resistance element 38 which is coupled at its other end to terminal 22 of transformer 16 as well as to one end of ballast resistor 40. The other end of ballast resistor 40 is connected to stationary contact arm 34. Ballast heating resistance element 38 is supported by stationary contact arm 36 and is insulated therefrom by an insulation layer 42. A movable contact arm 44 of switching device 28 is coupled to the other side of the parallel combination of ignitor and coil 12 and is mechanically biased to make electrical connection with stationary contact arm 36 by connecting linkage 46 and spring 48, as shown in FIG. 1.

Movable contact arm 26 is generally L shaped and extends through an opening 50 in linkage member 46 to a position adjacent the cantilevered end of a bimetallic element 52 which is mounted within heating proximity of ballast heating resistance element 38. The linkage member thus provides lost motion coupling, to be more fully explained below.

The operation of the system will be described with reference to FIGS. 2 and 3, as well as FIG. 1, wherein like reference numerals are used to refer to like components throughout. The three figures show the time sequence of operation of the preferred embodiment from the time the system is initially energized to the time when fuel flow as well as burner ignition are established.

Referring now to FIG. 1, the system is initially energized by the closure of switch from its open position as illustrated by the dashed line in the drawing. Switch 20 may be operated either manually or automatically in accordance with the particular requirements of the installation. It may, for example, be operated indirectly in response to a thermally sensitive device which monitors the temperature of the area to be heated. The resulting current from electrical power source 18 induces a voltage in the secondary winding of transformer 16 which appears across terminals 14 and 22. It is noted that transformer 16 may be either a step-up transformer, a step-down transformer or a one to one isolation transformer depending upon the particular installation. The voltage appearing at terminals 14 and 22 establishes a flow of current from terminal 14 through the series circuit of ignitor 10, movable contact arm 44, the contact of stationary arm 36, and heating element 38 to terminal 22. The voltage drop across ignitor 10 appears across holding coil 12 due to the parallel connection. Since the ignitor initially has a low temperature, its resistance will be small as compared to that of the ballast heating element, and thus its voltage drop will be insuflicient to energize coil 12.

The current flow causes heating of element 38 which, in turn, causes bimetallic element 52 to move down whereupon movable arms 26 and 44 move to the position shown in FIG. 2.

Continuing with reference to FIG. 2, it can be seen that the movement of bimetallic element 52 opens the connection between movable contact arm 44 and stationary contact arm 36 which thereby disconnects heating element 38 from the circuit. It is noted that the system is designed so that the residual heat from element 38 is sufiicient to cause bimetallic element 52 to continue moving so as to complete the electrical connection between movable arm 44 and stationary arm 34. In the embodiment shown in the drawings, this function is provided by arranging the bimetallic element 52 and the heating element 38 so that the bimetallic element moves toward the heating element. Therefore, the decreasing distance between the bimetallic element and the heater insures completion of the desired switching. Various other well known devices may be employed in the circuit to perform this function such as snap mechanisms, over center springs, and the like.

Movement of the bimetallic element to the position shown in FIG. 2 causes movable arm 44 to electrically contact stationary arm 34 thereby substituting ballast resistor 40 for ballast heating element 38. At the same time the current flow through ignitor 10 causes it to heat to fuel igniting temperatures whereupon its resistance increases to produce a voltage drop thereacross which is suflicient to energize holding coil 12 which in turn maintains linkage arm 46 in the position shown in FIG. 2. Movement of the bimetallic arm also serves to open the electrical connection between stationary arm 34 and movable arm 26, thus removing the energization winding of fuel valve 24 from the circuit and preventing its actuation until the bimetallic element returns to its normal ambient temperature position.

Referring now to FIG. 3, the cooling of bimetallic element 52 permits movable arm 26 to electrically contact stationary arm 34 to thereby place the electromagnet fuel valve 24 in parallel with ballast resistor 40 for energization. Thus a flow of fuel is established for ignition by ignitor 10 in fuel burner 32. As seen in FIG. 3, the lost motion coupling provided by the aperture 50' in linkage arm 46 permits holding coil 12 to maintain movable arm 44 in contact with arm 34 after bimetallic element 52 has cooled to ambient temperatures. Since movable arm 44 is mechanically biased away from arm 34, as shown in FIG. 1, a decrease in the energizing voltage across holding coil 12 will cause arm 44 to drop out thus removing the electrical actuation potential from the fuel valve 24 to effectuate rapid fuel shut-off. Since the potential across holding coil 12 is determined by the resistance of ignitor 10 which in turn is directly proportional to its temperature, the system is designed to produce a sufiicient voltage on the terminals of the holding coil 12 for energization only when the temperature of the electric ignitor is above fuel igniting temperatures. Any malfunction in the ignitor will therefore directly control the fuel flow to the burner to prevent raw fuel leakage.

In summary, this invention provides a simple, yet reliable, electric ignition system wherein the ignitor acts as a fuel igniting device as well as a rapid acting heat sensing element. In this manner, the fail-safe features of such a system are increased while the number of components required is reduced. This invention therefore makes electric ignition systems available for many diverse applications requiring high safety and low production cost.

Inasmuch 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 in nature and not in a limiting sense.

What is claimed is:

1. In an electric ignition system for a fuel burner, the combination comprising:

an electrical power source;

electric ballast means;

an electromagnet valve coupled in parallel with said ballast means and adapted to control a flow of fuel to the burner;

an electric ignitor adapted to be located adjacent the burner, said ignitor having a positive temperature coefiicient of resistance;

an electromagnetic relay electrically coupled in parallel with said electric ignitor to form a parallel network, said relay being energized by a voltage having at least a particular value;

a set of normally-open contacts coupled to said electromagnetic relay and adapted to be closed when said relay is energized, said normallyopen contacts being electrically coupled in series with said electric ballast means and said ignitor across said electrical power source for energization thereby; and

said parallel network having a voltage drop thereacross which is directly proportional to the temperature of said ignitor and has a value equal to said particular value when said ignitor is above fuel igniting temperatures.

2. The invention as recited in claim 1, further including a resistive heating element; and a set of normally-closed contacts coupled to said electromagnetic relay and adapted to be open upon energization of said relay, said normallyclosed contacts being electrically coupled in series with said resistive heating element and said ignitor across said electrical power source.

3. The invention as recited in claim 2, further including a bimetallic element located adjacent said resistive heating element and responsive to energization thereof to move from a first position to a second position; and switch means including a set of contacts responsive to movement of said bimetallic element, said contacts being closed when said bimetallic element is in said first position and being open when said bimetallic element is in said second position, said switch means electrically coupled in series with said electromagnet valve across said electric ballast means.

4. The invention as recited in claim 3, further including lost motion coupling means coupled to said bimetallic element, said set of normally-open contacts, and said set of normally-closed contacts, for closing said normallyopen contacts and for opening said normally-closed contacts when said bimetallic element moves from said first position to said second position.

5. An electric ignition system for a fuel burner comprising:

an electrical power source;

an electric ignitor coupled to said power source, having a voltage drop thereacross which increases with temperature and has a particular value when said ignitor is at fuel igniting temperature;

an electromagnetic relay electrically coupled in parallel with said electric ignitor, said relay being energized by a voltage having a value greater than said particular value;

a switch coupled in series with said ignitor mechanically biased to an open position and movable to a closed position said switch being located adjacent said electromagnetic relay and being adapted to be held in a closed position by said relay when it is energized;

control means coupled to said power source, said switch, and said electric ignitor, for providing a constant load and for moving said switch to its closed position in response to a flow of current through said ignitor after a predetermined delay time has elapsed;

an electromagnet valve for controlling a flow of fuel to the fuel burner;

a ballast resistor coupled in parallel with said electromagnet valve to form a parallel network, said parallel network being coupled in series with said switch and said electric ignitor across said power source for energization thereby when said ignitor is above fuel igniting temperatures.

6. The invention as recited in claim 5, wherein said control means includes a resistive heating element; and a bimetallic element located adjacent said resistive heating element and responsive to energization thereof to move from a first position to a second position.

7. The invention as recited in claim 6, wherein said control means further includes switch means including a set of contacts responsive to movement of said bimetallic element, said contacts being closed when said bimetallic element is in said first position and being open when said bimetallic element is in said second position, said switch means electrically coupled in series with said electromagnet valve across said electric ballast means.

8. The invention as recited in claim 7, further including means coupled to said ignitor and said bimetallic element for uncoupling said control means from said ignitor when said bimetallic element is in said second position.

9. The invention as recited in claim 8, wherein said means for uncoupling said control means includes a set of contacts mechanically biased to a closed position and adapted to be moved to an open position by the movement of said bimetallic element from said first position to said second position, said contacts being coupled in series with said resistive heating element and the parallel combination of said ignitor and said electromagnetic relay.

10. The invention as recited in claim 9 wherein said control means is coupled to said switch by lost motion coupling means.

References Cited UNITED STATES PATENTS 2,316,910 4/1943 Weber 43l66X 2,382,216 8/1945 Eskin et al. 43166X 2,621,647 12/1952 Pace 431-66X 3,196,929 7/1965 Miller et al. 431-66 FREDERICK L. MATTESON, JR., Primary Examiner R. A. DUA, Assistant Examiner U.S. Cl. X.R. 31794; 335-145

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