US3051862A - Gas ignitor - Google Patents

Description

Aug. 28, 1962 J. M. HOFF 3,051,862

GAS IGNITOR Filed Feb. 10, 1960 FIG. 1

GAS BURNER INVENTOR.

JOHN M. HOFF @Mn, 5W

ATTORNEYS United States Patent Office 3,051,862 Patented Aug. 28, 1962 3,051,862 GAS IGNITOR John M. Hofi, Mansfield, Ohio, assignor to The Tappan Company, Mansfield, Ohio, a corporation of Ohio Filed Feb. 10, 1960, Ser. No. 7,827 3 Claims. (Cl. 313-146) This invention relates to an improved electrode device for electric spark ignition of combustible gases, such as the gas-air mixtures used in domestic gas range burners, associated pilot burners and the like.

It is a primary object of the invention to provide an ignitor of this class which will operate efliciently at substantially lower voltage and current values than has commonly been thought necessary for the purpose, whereby the new ignitor is both more economical than conventional devices and safer in operation.

Another object is to provide such an ignitor having a very long service life, this characteristic resulting from a special feature of construction which affords compensation for the electrode erosion and loss which inevitably occurs.

Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawing setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed.

In said annexed drawing:

FIG. 1 is a diagrammatic view of a gas burner assembly, such as found in a domestic gas range, including an electric ignitor in accordance with the present invention;

FIG. 2 is an axial cross-section of the ignitor on an enlarged scale;

FIG. 3 is a similar section at right angles to the section shown in FIG. 2; and

FIG. 4 is an end view of the ignitor.

Referring now to the drawings in detail, the gas burner shown diagrammatically in FIG. 1 is a conventional oven burner of a domestic gas range having a series of ports along the bottom thereof for issue of the usual combustible mixture of gas and air supplied to such a burner. Beneath this oven burner, adjacent one end of the same, there is a pilot burner 11 which is again of conventional form and adapted to be supplied with the same gaseous mixture. An electric ignitor, designated generally by reference numeral 12, is here associated with the pilot burner 11 for controlled ignition of the gas-air mixture issuing therefrom when the supply of the mixture is established to the same, and the resulting pilot flame, of course, is used to ignite the main or oven burner.

This ignitor comprises a tubular housing 13, which has been made of stainless steel, with one end thereof flared to form a mouth 14 of conical section. As will appear more clearly below, the housing forms an outer electrode, and there is an inner electrode 15 in spaced relation within the housing. Such inner electrode is in the form of a wire of small cross-section and high electrical resistance extending generally along the axis of the housing 13 and being coiled into a plurality of turns 16 in the region of the housing just behind or .the rear of the mouth 14. The terminal portion 15 of the wire electrode at this end of the ignitor projects into the mouth 14 and extends interiorly thereacross at a considerable angle to the axis, with the extreme end or tip in close-spaced opposition to the conical inner surface of the mouth.

The wire electrode is bare and its turns 16 accordingly spaced apart and non-contacting.

At its other end, which is within the housing 13, the wire electrode 15 is bonded to a conductor 17 which projects from the rear end of the housing. Excluding the mouth 14, the space within the housing 13 and surrounding the enclosed portions of the wire electrode 15 and conductor 17 is filled with suitable thermal and electrical insulation 18. A filler of granular magnesium oxide has been used for the purpose, and the material is firm- 1y packed in the housing for support of the inner electrode and connected conductor therewithin.

A terminal strip 19 is suitably bonded to the project ing end of the conductor 17 and, as shown in FIG. 1, a wire connects this terminal to one side of the secondary winding of a step-up transformer 20, while the other side of such secondary winding is connected by 'a wire to the housing or outer electrode. The primary of this transformer is adapted to be connected to a conventional source of supply, and I have shown a simple switch 21 in the supply circuit to the transformer for control of the ignitor. Basically, the operation involves applying, by means of such transformer, high voltage at low current to the electrodes to create a spark therebetween effective to ignite the gas-air mixture supplied to the pilot burner 11, with the raw gas issuing from such burner being caused at least in part to flow over the mouth of the ignitor. The physical arrangement of the components may vary, but it is desirable to locate the ignitor so as to be in the stream of the raw gas to be ignited and yet not in the flame produced. For example, a relative positioning as shown will protect the ignitor from flame damage by virtue of the normal updraft resulting by combustion and corresponding direction of the flame.

For a number of reasons, it is significant that the inner electrode of the new ignitor is in the form of a wire of small cross-section; as a more specific example, this electrode has been made of nichrome wire of .032 inch diameter. Such dimensioning provides a highly concentrated spark and, since the wire electrode has such little mass, the flow of the gaseous mixture to the region of the spark is practically unobstructed. Moreover, heat is not readily conducted away from the tip of the wire electrode, as would be the case with a fairly heavy electrode, and such tip actually glows and promotes ignition on such account.

By virtue of these characteristics, it has been found that the new ignitor will operate properly, as compared to conventional devices on the same order, at considerably reduced voltage and current values. For example, whereas an ordinary spark ignitor may require 5,000 volts at .013 ampere, an ignitor constructed as aforesaid and including a wire electrode of the type and size specifically set forth will function with a supply of 2,000 volts at .008 ampere. The electrode gap in the new ignitor will generally be on the order of from .020 to .060 inch.

The end portion 15 of the wire electrode will in time become shortened by inevitable loss of metal, and the turns or coils 16 provide for lengthening the electrode to make up such loss. That is, the turns constitute, in effect, storage of the wire and, when the gap has increased to a point where loss of the spark cannot adequately be corrected by bending the initial exposed end length of the wire electrode, the wire is simply pulled from the insulative packing to extend the end turn until the initial exposed length is re-established. The encircling nature of the outer electrode, of course, facilitates positioning of the tip of the wire electrode, and the relatively large area of the surface available for the spark also keeps this electrode cool as a result of conductive dissipation of heat therein at the region of the spark, with deterioration of this electrode being negligible for practical purposes.

As workers in the art will appreciate, a typical gas cooking oven assembly in which the ignitor may be used will include various controls of known design and function for regulation, and possibly programming, of the oven operation. While these are not necessary to the present invention, it may be noted that the pilot burner will desira-biy incorporate a flame control of suitable type to prevent the flow of gas to the oven burner when the pilot is cold, or in other words, until after the pilot flame has been established by ignition. The ignitor energization should preferably be maintained for a definite interval to insure ignition, and the switch controlling the same can be of a type which will open only after a time delay for automatic provision of this feature.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

I, therefore, particularly point out and distinctly claim as my invention:

1. An electric spark ignitor for gaseous fuel burning devices, comprising an outer electrode in the form of a tube having a flared mouth at one end, an inner electrode in spaced relation within said outer electrode, said inner electrode being made of wire of small cross-section and high electrical resistance, the inner Wire electrode having an end portion within the mouth of the outer electrode at a substantial angle to the wall of the same and with its tip in closed spaced opposition to the inner surface of said wall, thereby to form a spark gap with the outer electrode, the wire inwardly with respect to the rnouth having a series of spaced storage turns therein, and being connected at its removed end to an external conductor, and a compacted mass of particulate thermal and electrical insulation material filling the space within the outer electrode about said turns and the extent of the wire electrode to the rear of the same, the wire electrode including the turns thereof being thus embedded in said material and being extensible from within the same at the gap-forming end to compensate for consumption of said wire electrode in use of the ignitor.

2. An electric spark ignitor for gaseous fuel burning devices, comprising a first electrode made of wire of small cross-section and high electrical resistance, a second electrode having a surface encircling an end position of said first electrode, the thus encircled end portion of the first electrode being at a substantial angle to said surface with its tip in close spaced opposition thereto to form a spark gap with the same, the first electrode wire having a plurality of storage turns therein for extension of the same to compensate loss of material at such spark tip thereof, and a compacted mass of particulate thermal insulation material surrounding such turns and the remote extent of the first electrode, the first electrode including the turns thereof being thus embedded in said material and being extensible from within the same.

3. An electric spark ignitor for gaseous fuel burning devices, comprising a first electrode made of wire of small crosssection and high electrical resistance, a second electrode having a surface disposed in close spaced opposition to an end of said wire to form a spark gap therewith, said first electrode having a plurality of storage turns formed therein and a terminal connection at its other end, the turns providing for extension of the Wire electrode relative to the terminal connection thereof to compensate for loss of material at the spark gap end to maintain proper gap dimension, and a compacted mass of particulate thermal insulation material surrounding such turns and the remote extent of the first electrode.

References Cited in the file of this patent UNITED STATES PATENTS 393,304 Haskins Nov. 20, 1888 895,030 Lang Aug. 4, 1908 1,290,121 Donat Jan. 7, 1919 2,241,295 Clark May 6, 1941 2,548,300 Garner Apr. 10, 1951 2,948,824 Smits Aug. 9, 1960 FOREIGN PATENTS 840,961 France Jan. 28, 1939

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