US2989660A - Electrical apparatus - Google Patents

Description

June 20, 1961 J. M. GRAHAM ETAL 2,989,660

ELECTRICAL APPARATUS Filed Sept. 29, 1953 Ticyl- INVENTORS James M. GRAHAM LOUIS H. SEGFILL QTTORNE 5 Unite v.

Delaware Filed Sept. 29, 1953, Ser. No. 382,902

6 Claims.

This invention relates to electrical apparatus and more particularly to devices adapted for use in creating sparks or arcs, such as may be useful in ignition systems for combustion engines and the like.

One of the objects of the present invention is to provide a novelly constructed sparking device of the type adapted for use as a spark plug or igniter plug in an engine ignition system.

Another object of the invention is to provide novel apparatus of the type embodying a shunted surface spark gap which is particularly adapted for use in a condenser discharge circuit for producing high energy pulses or sparks at relatively low voltage.

A further object is to provide a novel method of fabricating a sparking device of the type which may have a relatively narrow annular spark gap.

Still another object is to provide a novel spark gap assembly which makes possible the use of desirable electrode materials, the use of which has not been practical in comparable devices heretofore known.

The invention makes practical the use of smaller quantities of highly advantageous but expensive electrode materials.

A still further object is to provide a spark or igniter plug for use in an ignition system for combustion engines which is novelly constructed to insure a uniform annular spark gap and one which will withstand long and rugged use without danger of failures in operation.

Another object is to provide a sparking device of the above character which is so constructed as to substan tially eliminate any possibility of the leakage of gases therethrough.v

Another object is to provide a novel sparking device which is very compact and which presents only a small area tothehot gases of combustion in an engine cylinder.

Another object is to provide a novelly constructed sparking device which has a high pre-ignition rating and which is substantially non-fouling.

The above and further objects and novel features of the present invention will more fully appear from the following detail description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the. purposes of illustration only and are not intended as a definition of the limits of the invention.

In the drawings, wherein like reference characters refer to likeparts throughout the several views,

. FIG..1 is a longitudinal sectional view of one form of igniter plug embodying the present invention;

FIG. 2 is a bottom view of the device shown in FIG. 1;

FIG. 3 is an exploded view showing parts of the device of FIG. 1 prior tofinal assembly, some of said parts being in unfinished form for assembly purposes.

.The single embodiment of the invention illustrated in the drawings, by way of example, is in the form of a spark plug or igniter plug for use in the ignition system of a combustion engine, but it will be understood that the use of the invention is not so limited. The type of device illustrated may be used for ignition purposes in any combustion chamber, such as in the cylinders of a piston engine or in thecombustion chambers of jet and gas turbine type engines. Parts or all of the novel construction illustrated may also be used in other. environments as a spark gap, such as for controlling the flow of electrical States Patent energy in an electrical circuit, and particularly for controlling the discharge of electrical condensers.

In the form shown in the drawings, the igniter plug comprises a tubular metallic shell 10 which has external threads 11 by means of which the plug may be operably mounted in the wall of a combustion chamber, or the like. Other suitable known mounting means may, of course, be employed. An internal flange 12 at the lower end of shell 10 supports a novel spark gap assembly S which will be hereinafter more fully described. Extending upwardly from assembly S along the central axis of the shell is a spindle 14 which provides an input terminal 15 that may be connected to a source of electrical energy, such as a charged electrical condenser. The annular space within the shell above assembly S and around spindle 14 is filled with an insulating mass 16 and a sleeve 17 of ceramic or other suitable insulating material. The mass 16 may be formed by a glassy substance or the like having a high melting temperature, such as lead borosilicate glass, and serves as a seal and as a mechanical binder for the assembled parts. One suitable composition for the mass 16 comprises equal parts of lead oxide and Pyrex glass. A lead cobalt silicate glass frit may also be used. The mass 16 is rendered plastic by heat during assembly and compressed to a high density. Thin layers of mass 16 enter the small annular spaces between sleeve 17 and shell 10 and between said sleeve and spindle 14. The effects of differences in the coefficients of expansion of the parts are thus minimized. The upper end of shell 10 is internally threaded at 18 for receiving a gland nut or shielding barrel 19 which engages the outer end surface of sleeve or bushing 17 and complements the mass 16, if necessary, for holding the parts in assembled relation.

The novel spark gap assembly S comprehended by this invention comprises, in the form shown, an outer shell 20, the central portion of which has a close fit in shell 10 and rests upon flange 1'2. Preferably, shell 20 has a reduced portion at the outer or lower end thereof which has a force fit within said flange and terminates flush with the end of shell 10. The upper or inner end of assembly shell 20 is also reduced to providea thin wall section and an annular space 21 into which the insulating mass 16 extends. Shell 20 is provided at itsouter end with an internal flange 22 that serves as a seat or support for an annular disc or ring electrode 23. The latter is preferably made of a substance, such as tungsten, which will resist erosion or deterioration by electrical sparking, high heat and the products of combustion within the combustion chamber. The electrode may be and prefer: ably is soldered into shell 20 by means of silver solder, or its equivalent. The lower face of flange 22 may be tapered as shown, but this is not essential.

Centrally disposed within shell 20 is a center electrode support 24 having an enlarged head 25, which terminates flush with the outer ends of shells 10 and 20. The periphery of head portion 25 is preferably tapered oppositely to the taper of flange 22 to provide a tapered annular groove. Seated on the upper or inner surface of head portion 25 and closely surrounding the spindle of support 24 is a second annular disc or ring electrode 26 which may be soldered to the support 24, 25 and may be of tungsten or other suitable electrode material. The adjacent diameters, i.e., the inner and outer peripheries of discs or rings 23 and 26, respectively, are such that an annular spark gap 27 is provided therebetween. Said gap may be made quite wide or the same may be very small. In one practical embodiment, a gap as small as about .005 inch has been found desirable.

, Secured between shell 20 and electrode support 24 for accurately maintaining the same in concentric spaced relation is a ring 28 of rigid insulating material, such as aluminum oxide. This ring has a close fit around the spindle of support 24 and within shell 20. The lower face 29 of said ring is ground flat to provide good surface engagement . withelcctrode rings 23 and 26 andis treated with silver nitrate or its equivalent or is impregnated in any suitable manner with a metallic or other electrically conductive substance to render said surface highly resistive or semi-conductive to electrical current. Thus, although a voltage impressed across electrodes 23 and 26 may be too low to jump gap 27, it may nevertheless create a flow of energy through or along the semiconductive surface of ring 28 and thereby sufliciently ionize the gaseous medium in the gap to permit the low voltage to bridge the gap and create a spark or arc. When the energy is supplied by a charged condenser or its equivalent, the spark thus created may embody a substantial amount of energy even though the voltage is relatively low.

The gap assembly S is made into a rigid unit by spinning the edges of the thin walls of shell 20 and of the counterbored inner end of support 24 inwardly and outwardly, respectively, onto ring 28. Brass or other suitable washers 30 and 31 are preferably provided between the insulating spacer ring and the turned over portions of members 20 and 24. The upper surface of ring 28 is preferably stepped, as shown, to provide a safe creepage path or flash-over distance between the upper ends of shell 20 and support 24. The inner or upper portion of the assembly S is surrounded by and virtually embedded in mass 16. Thus, the latter not only serves as a seal to prevent the flow of gases from the combustion chamber, but also serves as means for mechanically positioning and securing the spark gap assembly S within shell 10.

For assembly purposes, shells 10.and 20 are initially made with extensions or skirts 33 and 34, respectively, and central electrode support 24 is provided with an extension 35. A ring 37 is located around extension 35 within skirt 34 and, if desired, ring 37 may be in the form of a flange formed integrally with extension 35. These extensions and ring 37 are carefully machined to accurately fit within one another so that when the parts are assembled, accurate concentricity thereof, and hence uniformity in the width of gap 27 will be assured. This concentricity is of greatest importance when the width of gap 27 is small. The electrode rings 23 and 26 are first soldered to shell 20, 34 and support 24, 35 with a high melting point solder, such as silver solder. The shell and support are then assembled with spacer ring 28, washers 30 and 31, and centering ring 37. With the parts of the electrode assembly thus held in assembled relation, the upper edges of shell 20 and support 24 are spun into firm engagement with Washers 30 and 31. The electrode assembly is then placed in shell 10, the skirt 34 having a drive fit within extension 33. Spindle 14 is then inserted with the lower reduced end thereof threaded into the counter-bore in support 24. The spindle may have a force fit in support 24, or a solder ring may be interposed between a downwardly facing shoulder on the spindle and the upper end of support 24 to insure a good electrical connection and serve as an anchor for the spindle. The bore of shell is then filled to a point below a shoulder 36 with powdered glass or other suitable fusible insulating material having a high melting point and bushing 17 is seated on top of the powdered mass. Heat is then applied, such as by electrical induction or by gas flames applied to the outer surface of shell 10, to fuse the powdered mass within shell 10. While said mass is in a plastic or molten state, pressure is applied to press bushing 17 against said mass and firmly compress the latter into all available space between bushing 17 and the electrode assembly S, and into and around said bushing. The application of pressure is continued while the parts are permitted to cool. After the parts have cooled, the extensions 33, 34 and 35 76 are machined off, leaving the structure as illustrated in full lines in FIG. 1. Nut 19 may then be screwed into place against bushing 17 to complement the mass 16.

There is thus provided by the present invention a novel spark gap device which may be fabricated in accordance with a novel method to insure accurate concentricity of electrodes to provide a small, uniform annular spark gap. The novel construction provided also insures against gas leakage therethrough which would reduce the operating efficiency and life thereof. Additionally, the structure comprehended is of a sturdy construction which will withstand physical shock and vibration as well as wide and rapid changes in temperature. The materials used are such that erosion by electrical sparking is reduced to a minimum, thereby prolonging the useful life of the device. The small number of parts employed are all of simple construction which may be inexpensively manufactured and readily assembled.

Although only a single embodiment of the invention has been illustrated in the accompanying drawings and described in detail in the foregoing specification, it isto be expressly understood that the invention is not limited thereto. For example, materials other than those specifically mentioned as being suitable may be used. Platinum, alloys of platinum and other materials known to be well adapted for making electrodes may be used inlieuof tungsten and the silver deposited on the lower face of insulator 28 may be replaced by other materials such as carbon, graphite and the like. Various other changes, such as in the specific design and arrangement of the parts illustrated may also be made without departing from the spirit and scope of the invention as the same will now be understood by those skilled in the art.

What is claimed is:

1. In an electrical sparking device, a tubular shell having an internal flange at one end thereof, a spark gap assembly comprising a tubular shell member having a sliding fit in said shell and a pilot extension having a tight fit in said flange, said member being seated on said flange, center electrode means in said member and in spark gap relation therewith and an insulating sleeve interposed between said member and said center electrode means, a conductor extending through said shell from said center electrode means, and a mass of insulating material set from a plastic state under pressure within the shell and completely filling the annular space in said shell immediately above said assembly and around said conductor.

2. A spark gap device comprising a tubular shell having an internal flange at one end thereof, a spark gap assembly seated on said flange and comprising a tubular shell member having an internal flange at one end thereof, an annular electrode seatedon said flange, a center electrode support extending through said member, said support having an enlarged head portion and a spindle, an annular center electrode seated on said head portion within and in spark gap relation to said first-named annular electrode, and an insulating sleeve seated on said annular electrodes and surrounding said spindle within said memher, the other end of said member having an internal flange engaging a shoulder on said sleeve and the upper end of said spindle having an external flange engaging the end of said sleeve, whereby the parts are held in assembled relation, a pilot extension of said member having a force fit in said shell flange, and a mass of insulating material set from a plastic state under pressure within the shell and filling the space in said shell immediately above said assembly around an extension of said center electrode support, said mass having intimate contact with said shell for holding the shell and assembly in assembled relation.

3. A spark gap device as defined in claim 2 wherein said mass is a glass having a high melting point, such as lead borosilicate glass.

4. The method of fabricating a spark gap assembly which includes the steps of making a tubular shell member having an internal shoulder and a cylindrical pilot extension, centrally supporting a center electrode support with a pilot extension in a pilot in said cylindrical pilot extension, locating concentric electrode rings in the same plane on said shoulder and on a shoulder on said center electrode support, inserting an insulating sleeve in said shell member on said electrode rings and around said center electrode support, turning the end of said member inwardly over said sleeve and turning the end of said center electrode support outwardly over said sleeve.

5. The method of fabricating a spark gap device which includes fabricating a spark gap assembly as defined in claim 4, inserting said assembly into a tubular shell having a tubular pilot extension in which the pilot extension on said shell member has a force fit, securing said assembly in said shell, and thereafter machining off said pilot extensions.

6. The method of fabricating a spark gap device as defined in claim 5 wherein the step of securing said assembly in said shell includes the steps of placing a fusible insulating material in the shell above the assembly, fusing said material by application of heat, and applying pressure to said fused material while the latter cools to solidification.

References Cited in the file of this patent UNITED STATES PATENTS 1,009,867 Terry Nov. 28, 1911 1,272,954 Horning July 11, 1918 1,999,785 Rohde Apr. 30, 1935 2,408,642 Hopps et al. Oct. 1, 1946 2,497,862 Chuy Feb. 21, 1950 2,501,826 McCarthy Mar. 28, 1950 2,572,209 Smits Oct. 23, 1951 2,615,441 Bychinsky Oct. 28, 1952 2,625,922 Smits Jan. 20, 1953 2,684,665 Tognola July 27, 1954 2,747,123 Tognola May 22, :1956 2,861,014 Sheheen Nov. 18, 1958 2,874,322 Bychinsky Feb. 17, 1959 FOREIGN PATENTS 631,386 Great Britain Nov. 2, 1949 868,459 France Oct. 6, 1941

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