US2575113A - Igniter - Google Patents

Description

T. H. LENNOX Nov. 13, 1951 IGNITER Filed May '7, 1949 BALLAST TYPE lGN/TEfi Z0 VOLTS 0O VDLTS CONSTANT IST TIME IN SECONDS Inventor Thomas H. Lennox by Hrs Attorney Patented Nov. 13, 1951 IGNITER Thomas H. Lennox, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Application May 7, 1949, Serial No. 92,021

8 Claims. 1

My invention relates to resistance type electrical igniters for oil furnaces and the like and has for an object the provision of an igniter of this type which, upon being energized. increases rapidly in temperature to a predetermined value and then maintains substantially a uniform temperature as long as it remains energized.

Another object of the invention is to provide an igniter having an outer sheath around the heat generating resistance conductor to provide.

protection from the corrosive action of the burning fuel in the heating chamber.

A still further object of my invention is the provision of an igniter which is inherently selfprotecting against damage due to variations in the applied voltage and variations in the starting temperature.

In carrying out my invention in one form, I provide an igniter which is composed of two parts, an ignition unit and a ballast unit. The ignition unit is made of a resistance conductor havinga relatively high specific resistance surrounded by an insulated protective sheath. The ballast unit is composed of a combination of resistance conductors having a relatively low specific resistance at normal temperatures but a high temperature coeflicient of resistance so that its specific resistance is greatly increased at higher temperatures. These resistance conductors are enclosed in a second insulated protective sheath along with a heater wire which is responsive in the amount of heat it dissipates to the supply voltage for the igniter. In addition, there is a thermostat on the ballast which is responsive to the temperature of the ballast. The contacts of the thermostat are connected in series with the ignition unit and the combination of resistance conductors in the ballast unit, whereby, if the ballast is not at a proper starting temperature,

the contacts of the thermostat are open and the igniter cannot be energized.

For a clearer and more complete understanding of my invention, reference should be had to the accompanying drawing, Fig. l of which is a schematic diagram of a preferred embodiment of the invention, while Fig. 2 illustrates, by means of curves, the improved characteristics of my igniter as compared to those of conventional igniters.

Referring to Fig. l of the drawing, the ignition unit portion of the igniter is designated generally by the numeral I0, while the ballast portion is designated by the numeral II. The ignition unit Ill has an outer metallic sheath I2 which may be tubular in form and bent in the shape of a hairpin. A sinuous resistance heating conductor I3, having a high specific resistance but a low coefficient of resistance, is positioned within the sheath I2. Resistance conductor I3, which is shown as helical in form, is provided with two terminal conductors I4, which extend out the ends of the sheath, or casing I2. Heating resistance I3 and conductors I4 are secured centrally of the sheath I2 by means of suitable electrical insulating material I5, which is preferably magnesium oxide powder. The magnesium oxide powder is compacted in the sh ath I2, surrounding and embedding the resistance heating unit I3 and terminal conductor I4.

Ihe compacting of the magnesium oxide powder is preferably performed by reducing the diameter of the sheath by rolling or swaging after the ignition unit has been assembled, but before it is bent into the hairpin shape. The sheath, resistance heating element, terminal connectors and insulating material are thus combined into a structurally homogenous unit which may be bent as desired into various shapes to facilitate the use of the unit for a particular purpose or the concentration of heat in a particular region. The heating unit In is sealed at the extremities of the insulating material I5 by a suitable means, such as mica retainers IS, in order to retain the insulating material within the ignition unit. A circular flange II, through which the two legs of the heating unit protrude, is provided to secure the ignition unit Ill in a furnace or other similar apparatus.

The ballast section II is composed of an outer tubular sheath I8 with a terminal portion at one end comprising a short length of coaxial conductor, and a common terminal I9 for three resistance conductors at the opposite end. A heater resistance wire 20 is centrally positioned in the ballast, being connected between common terminal I9 at one end of the ballast and the center member 2I of the coaxial terminal at the other end. Spaced around heater wire 20 is a double helical coil composed of two resistance conductors 22 and 23 of dissimilar materials. Resistance conductors 22 and 23 are of substantially the same total length and are connected in parallel, both being connected between common terminal I9 and the outer portion 24 of the coaxial terminal at the opposite end of the ballast.

Resistance conductor 22 is of a material having a relatively low specificresistance in comparison with the material of resistance heating unit I3 but, at the same time, having a high positive coefflcient of resistance which causes its resistance to increase rapidly as its temperature is increased. Resistance conductor 23 is of a material having a high specific resistance and a relatively low coefllcient of resistance, both values being substantially equal to the like characteristics of resistance heating conductor l3. Resistance conductors 22 and 23 and heater wire are maintained in the correct positions in the ballast unit by insulating material 25, which is suitably compacted around them. Material 25 is preferably magnesium oxide powder which is compacted by reducing the diameter of sheath It! by swaging or rolling after assembly, in a manner similar to that previously described for ignition section H]. In order to retain the magnesium oxide powder within the ballast, it is sealed at the end having the common terminal I 9 by a mica retainer 26 and at the opposite end by a mica retainer 21. Coaxial terminal members 2| and 24 are separated by a layer 28 of electrical insulating material, preferably compacted magnesium oxide powder, which has a mica retainer 43 at the outer extremity thereof.

While ballast unit II is illustrated in Fig. l in the form of a straight rod-like member, it is possible, in order to adapt the ballast to a particular installation, to form the ballast unit into any one of a variety of shapes after it has been swaged. The ignition unit In may also be formed into shapes other than the hairpin shape which is illustrated, if desired.

On the outer surface of sheath l8 of ballast H is located a thermostat composed of an inner member 29 and an outer bi-metal member 30. Members 29 and 30 are both secured to sheath I8 by a suitable means, such as brazing or welding, to form a good heat conductive joint. Bimetal 3|! has an extension 3| of electrical insulating material secured thereto in a suitable manner, such as by a rivet 32. Member 29 has an extension 44 of electrical insulating material secured thereto by a rivet 45 with a contact member 34 located in an opening near the end of extension 44. Extension 3| has a contact member 33 of conducting material positioned in an opening therein to enable contact 33 to engage contact 34. If the temperature of ballast unit II is above a predetermined value, bi-metal strip 30 causes contact 33 to engage contact 34. If the temperature of the ballast is below this predetermined value, contacts 33 and 34 are parted.

In the operation of the igniter, it is supplied with electrical energy, preferably alternating current, from electrical supply mains 35 and 36. Heater wire 20 in the ballast unit is connected directly across the mains by means of conductors 31 and 38 and is, therefore, energized whenever mains 35 and 36 are energized. Heater wire 20 is of low wattage and dissipates a relatively small amount of heat. The heat so dissipated, however, is proportional to the square of the voltage between mains 35 and 36. Therefore, heater 20 maintains ballast II at a temperature which is responsive to the system voltage; the significance of this feature is explained later.

Ignition section I0 and the ballast H are connected in series across electrical mains 35 and 35 by means of a circuit composed of conductor 31, terminal I9, resistance conductors 22 and 23 in parallel, outer member 24 of the coaxial terminal of the ballast, a conductor 46, contacts 34 and 33, a conductor 39, a terminal member M of the heating unit, heating resistance |3, the other terminal H, a conductor 40, a switch 4|, and a conductor 42. To initiate operation of the igniter, switch 4| is closed, preferably by the automatic control circuit of a fuel oil furnace or other similar apparatus. This causes current to flow through the circuit Just described, including resistance conductors 22 and 23 and resistance heating conductor l3, providing that contacts 83 and 34 on the thermostat are in engagement.

Assuming that contacts 33 and 34 are engaged when switch 4| is closed, then electrical current flows through the ballast unit H and the ignition unit ID in series. The initial potential drops in the two units are proportional to the ratio of starting resistances of the two units. Inasmuch as the active portion of ballast comprises two resistance conductors in parallel, one of which member 22 has a relatively low specific resistance at ordinary temperatures, the portion of the total initial potential drop which takes place in ballast II is relatively small. However, as ballast ll becomes heated from the dissipation of heat therein by resistance conductors 22 and 23, the specific resistance of member 22 increases from its initial relatively low value. since it has a high c0- eflicient ofv resistance. This causes an increase in the total resistance of ballast causing it to assume a larger portion of the total potential drop. This, in turn, means that a smaller portion of the potential drop takes place in heating element i3 in unit I0, whereby the initial high rate of heat generation by unit H], which occurs when switch 4| is first closed, is gradually reduced. Thus, igniter unit I0 is caused to heat up rapidly at first, with the rate of heating being gradually reduced so thatthe ignition unit does not become overheated.

In one typical igniter embodying my invention, an alloy of nickel and chromium having a relatively high specific resistance and a relatively low coeificient of resistance was used for resistance conductor I3 in the heating unit and resistance conductor 23 in the ballast unit. Resistance conductor 22, connected in parallel with resistance conductor 23, was made of an alloy of nickel and iron having a relatively high positive coefiicient of resistance. The resistance of member 22 is approximately one quarter of the resistance of member 23 at '70 degrees F. At the maximum temperature to which the ballast rises during ignition, the resistance of member 22 is approximately equal to the resistance of member 23 at that temperature. In addition, the resistances of the ignition unit and the ballast unit are proportioned so that the resistance of heating element I3 is approximately equal to the total resistance of resistance conductors 22 and 23 in parallel under conditions existing when the temperature of the ignition unit has leveled oil during the ignition period.

Utilizing this typical igniter, I have plotted curves of the variation of the temperature of ignition unit ID with time. Two such curves are shown as curves A and B in Fig. 2 on the drawing. Curve A was taken with an applied voltage of 120 volts, while curve B was taken with an applied voltage of volts, these voltages being two which might be encountered in a typical oil furnace installation in a private residence. It can be seen from these curves that the temperature rises rapidly at first, reaching temperatures higher than 1800 F. in both cases in less than 60 seconds, and then levels off at a temperature slightly less than the peak value. It will be noted also that the peak value does not exceed 2000 F. in either case.

In contrast to curves A and B, I have shown in Fig. 2, curves C and D, which were taken with a comparable igniter of the constant resistance type; that is, one which does not have the varying resistance ballast of my invention and which, therefore, has a constant heating rate over the entire temperature range. At 120 volts, this igniter required approximately 90 seconds to reach 1800 F., while at 100 volts it rose to approximately 1750 F. in 150 seconds. It can be seen, therefore, that the igniter embodying my invention produces ignition temperatures much more quickly than a constant resistance igniter, and it accomplishes this without excessive peak temperatures which might damage the igniter.

It will be observed also from Fig. 2 that the leveling of! temperatures for the igniter in which my invention is incorporated are more nearly uniform for diflerent volta'es than is the case for the constant resistance igniter. This is due to the action of preheater 20 in the ballast l I. Wire 20 is connected directly across electrical supply mains 35 and 36 and is energized continuously, as long as mains 35 and 36 are energized. The heat generated by wire 20 is proportional to the square of the current flowing therein, and the current is proportional to the applied voltage; therefore, the temperature of ballast ll varies responsively to the voltage across lines 35 and 36, the temperature of the ballast being lower for a lower voltage and higher for a higher voltage. This means that the starting resistance of resistance conductor 22 is lower for a lower than normal supply voltage causing heating element l3 to assume a greater than normal portion of the voltage drop, thereby generating more heat and raising the temperature of igniter unit H) at a faster rate than would be the case if voltage compensation were not provided for the ballast. If the supply voltage is greater than normal, the temperature of ballast II is maintained at a greater than normal value by preheater 20, which increases the starting resistance of resistance conductor 22. This decreases the heating rate of resistance conductor i3 from what it would be if voltage compensation were not provided for the ballast. Thus, the voltage compensation of ballast I l by preheater 20 tends to make the heating rate of ignition unit I0 uniform regardless of the applied voltage.

Furthermore, the voltage compensation of the ballast section also makes the leveling off temperature of the igniter more uniform. If the supply voltage is higher than normal, the presence of heater 2|! in the ballast makes the resistance of resistance conductor 22 more than it would otherwise be, even after ignition conditions are reached; therefore, the energy dissipated by resistance conductor 13 is less and the igniter levels oil at a lower temperature than it would if heater 20 were not present. Conversely, if the supply voltage is low, the reduced heat in ballast ll causes ignition section In to dissipate a larger than normal percentage of the energy, making it level oil at a higher temperature than would otherwise be the case.

The thermostat on ballast l i is to protect ignition unit I!) in case ballast l I is, for some reason, at too low a temperature to operate properly when switch M is closed. If the temperature of ballast H is below a certain predetermined value, contacts 33 and 34 are parted, making it im possible to complete the ignition circuit. It the temperature of ballast II were too low, and the ignition circuit were completed, the starting resistance or resistance conductor 22 might be so small that heating element l3 would become overheated before the resistance of member 22 had built up suificiently to prevent such overheating. A condition when the temperature of the ballast is too low for proper operation might occur if the electrical supply circuit has been deenergized, allowing heater 20 to cool. If such should occur, it would not be possible to close the ignition circuit, even after restoration of potential to conductors 35 and 36, until heater 20 has been energized long enough to bring ballast ll up to proper operating temperature. When the proper temperature is attained, contacts 33 and 34 close, making it possible to energize the igniter circuit by closing switch 4|.

One modification of my invention is to eliminate resistance conductor 23 from the ballast unit H. This increases the efiect that the conductor 22 with its high temperature coeificient of reistance has on the operation of the igniter. This means, in turn, that if conductor 22 is selected so that the peak temperature of the ignition unit I0 is substantially the same as that indicated in Fig. 2 for a corresponding voltage, then the leveling-off temperature following the peak for the modified igniter will be less than that shown in Fig. 2. In other words, the effect of resistance conductor 23 in the ballast unit is to counteract in part the effect of resistance conductor 22 in order to produce a leveling-oil temperature which is approximately the same as the peak temperature. In some circumstances, however, a lower leveling-off temperature is not ob- .iectionable and in these cases this modified em bodiment of my invention may be used.

While I have described a typical igniter embodying a preferred form of my invention in which an alloy of nickel and chromium is utilized for resistance conductors l3 and 23, other materials having similar high specific resistance and low coefilcient of resistance characteristics may also be used for these members. An example of another such material is an alloy of chromium, aluminum and cobalt. Similarly, other materials, such as pure nickel, for example, which have a high coefllcient of resistance, and a relatively low specific resistance at normal temperatures, may be substituted for resistance conductor 22 without departing from the spirit and scope of my invention. Therefore, while I have illustrated and described one preferred embodiment of my invention, together with one modification thereof, it should be understood that I intend to cover, by the appended claims, all modifications which fall within the true spirit and scope of my invention.

I claim:

1. An igniter having a ballast section comprising two resistance conductors in parallel, one resistance conductor being of a material having a relatively high specific resistance and a relatively low coeflicient of resistance, the other resistance conductor being of a material having a rela tively low specific resistance and a relatively high coeflicient of resistance, a preheater for said ballast section and a thermostat responsive to the temperature of said ballast section, an igniter section comprising an enclosed resistance conductor of a material having a relatively high specific resistance and a relatively low coeiiicient of resistance, and means for connecting the resistance conductors of said ballast section in series electrically with said thermostat and the resistance conductor 01" said igniter section.

2. An igniter comprising a first electrical re= sis ance conductor having a relatively hi h specific resistance and a relatively low coeiiicient oi resistance in series with a second electrical resistance conductor having a relatively low specific resistance and a relatively hi h coeiflcient of resistance. the resistance of said second conductor being substantially less than the resistance of said first conductor at a normal unheated temperature. whereby when said igniter is connected to a source of electrical energy most of the energy is dissipated initially in said first conductor but as the igniter temperature increases the resistance of sa d second conductor increases. increasing the energy dissipated by said second conductor and causin said first conductor to dissipate less energy, thereby preventing the temperature of said first conductor from exceeding a predetermined value. and an electric preheater for said second resistance conductor connected to be. energized respons vely to said source of electrical energy to compensate for potential variations in said source.

3. An igniter comprising a first electrical resistance conductor having a relatively high specific resistance and low coefficient of resistance connected in circuit with a parallel pair of resistance conductors. one-of said pair having a relatively low specific resistance and high coefficient of resistance. the other of said. pair having a relatively high specific resistance and low coefiicient of resistance. the resistance of said first conductor being substantially greater than the resistance o said pair at normal unheated temperatures. whereby when said igniter is connected to a source of electrical energy most of the energy is dissipated initially in said first conductor but as the temperature of said parallel pair increases the resistance of said pair increases. thereby increasing the energy dissipated by said pa r and reducing the energy dissipated by said first conductor. thus preventing the temperatu e of said first conductor from exceeding a predetermined value.

4. An igniter comprising a first electrical resistance conductor having a relatively high specific res stance and a relatively low coefiicient of resistance connected in circuit with a parallel pair of resistance conductors of substantially equal length, one of said pair having a relatively low specific resistance and relatively high coefiicient of resistance. the other of said pair having a relativel hi h specific resistance and relatively low coefiicient of resistance, the. dimensions of said resistance conductors being such that the resistance of said parallel pair is substantially less than the resistance of said first conductor at normal temperatures and approximately equal thereto under ignition conditions, whereby when said igniter is connected to a source of electrical energy most of the energy is dissipated initially in said first conductor but as the temperature of said parallel pair increases the resistance of said pair increases, thereby increasing the energy dissipated by said pair and reducing the ener y dissipated by said first conductor, thus causing the temperature of said first conductor to rise rapidly to a predetermined ignition temperature and level off at substantial- 1y said ignition temperature.

5. An oil burner igniter device comprising a ballast unit having an outer tubular metal sheath, 2. layer of electrically insulating heat conductive material immediately inside said meta1 sheath, and a center member embedded in said material within said sheath substantially centrally of the sheath and projecting at each end thereof, said center member comprising a concentric terminal composed of an inner connector and an outer connector insulated from each other at one extremity of said center member, a terminal at the opposite extremity of said center member, a heater wire connecting said terminal and the center connector of said concentric terminal, and two resistance conductors of dissimilar metals connected in parallel between said terminal and the outer connector of said concenrtic terminal, an ignition unit comprising a second metal sheath of substantially circular cross section, a second layer of electrically insulating heat conductive material immediately inside said second sheath, and a second center member embedded in said second layer located substantially centrally of said second metal sheath and projecting at each end thereof, said second center member comprising a terminal portion at each extremity and a length of resistance heating conductor connected between said terminal portions, and means for connecting the heating conductor in said ignition unit in series with the two resistance conductors of dissimilar metals in said ballast unit.

6. An igniter for oil furnaces and the like comprising an ignition unit for insertion in the furnace chamber, a ballast unit for location externally to the furnace chamber, and electrical connections joining said ignition unit and said ballast unit in series, said ignition unit comprising an insulated resistance conductor having a relatively hi h specific resistance and a relatively low coefiicient of resistance within a protective sheath, said ballast unit comprising an insulated resistance conductor having a relatively low specific resistance when unheated and a relatively high positive coefiicient of resistance in parallel with a second insulated resistance conductor having a relatively high specific resistance and a relatively low coefficient of resistance within a protective sheath, whereby when electrical potential is applied to said igniter said ignition unit dissipates most of the energy initially and increases rapidly in temperature, said ballast unit dissipating an increasing portion of the energy as the temperature of the ballast also increases, thereby causing the temperature of said ignition unit to level ofi after rising rapidly to a predetermined value.

7. An igniter for oil furnaces and the like comprising an ignition unit for insertion in the furnace chamber, a ballast unit for location externally to the furnace chamber, and electrical connections joining said ignition unit and said ballast unit in series, said ignition unit comprising an insulated resistance conductor having a relatively high specific resistance and a relatively low coefficient of resistance within a protective sheath, said ballast unit comprising a pair of resistance conductors of dissimilar materials connected in parallel, one of said pair having a relatively low specific resistance when unheated and relatively high coefiicient of resistance, the other of said pair having a relatively high specific resistance and a relatively low coefiicient of resistance, the dimensions of the resistance conductors in said ignition unit and in said ballast unit being proportioned so that when electrical potential is applied to said igniter said ignition unit dissipates most of the energy initially and increases rapidly in temperature, said ballast unit dissipating an increasing portion of the energy as the temperature of the ballast also increases, thereby causing the temperature of said ignition unit to level 011 after rising rapidly to a predetermined value.

8. An electrical igniter for oil furnaces and the like, having an ignition unit comprising a sinuous heating element of material having a relatively high specific res stance and a relatively low temperature coeflicient of resistance, a pair of terminal conductors connected respectively to the ends of said heating element, a layer of compacted magnesium oxide powder embedding said heating element and surrounding portions of said terminal conductors, and a tubular metallic sheath around said layer of magnesium oxide powder, said magnesium oxide powder being compacted by swaging the ignition unit assembly after insertion of the component parts. within said sheath, an elongated ballast unit comprising a heater wire for varying the temperature of said ballast unit responsivelv to the igniter operating voltage. a double helical coil positioned coaxially around said heater wire composed of two resistance conductors of dissimilar materials of substantially equal length, one resistance conductor having a relatively high specific resistance and arelatively low temperature coefflcient of resistance, the other resistance conductor having a relatively low specific resistance at ordinary temperatures and a relatively high positive temperature coeflicient of resistance, a common terminal at one end of said ballast unit to which said heater wire and said two resistance conductors are connected, 9. concentric terminal at the op osite end thereof, said heater wire being connected to the inner portion of said concentric terminal, said resistance conductors being connected to the outer portion of said concentric terminal, a layer of compacted magnesium oxide powder surrounding and embedding said heater wire and said resistance conductors, and a tubular sheath around said magnesium oxide powder, said magnesium oxide powder being compacted by swaging the ballast unit assembly after insertion of the component parts within said sheath, a thermostat positioned on the outer surface of? said sheath responsive to the temperature of said ballast unit, said thermostat having contacts which are closed when the temperature of said ballast unit is above a predetermined minimum value, means including the outer portion of said concentric terminal for connecting the heating element in said ignition unit through the contacts of said thermostat to the resistance conductors of said ballast unit, switch means for connecting said heating element and said resistance conductors to a source of electrical potential, and means including the inner portion of said concentric terminal for connecting said heater wire to said source.

THOMAS H. LENNOX.

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

UNITED STATES PATENTS Num er Name Date Re. 10,944 Weston July 17, 1888 1,359,400 Lightfoot Nov. 16, 1920 1,393,325 Smith Oct. 11. 1921 1,400,410 Bossu Dec. 13, 1921 1,954,832 Ruben Apr. 17, 1934 2,005,832 Vidalie June 25, 1935 2,375,058 Wiegand May 1, 1945

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