US2914693A - Spark plug construction - Google Patents

Description

Nov. 24, 1959 E. w. MEYER, JR., EI'AL 2,914,693

SPARK PLUG CONSTRUCTION Filed Nov. 29, 195'? YER JR. 659%: E. SPAULDING JR. 4, 5

ATTORNEYS PICIJ: I EARL W'ME mmvroxs.

of the conventional ignition system. y r This invention alsoincludes a spark plug havinga spark,

"2,914,693 SPARK PLUG CONSTRUCTION I u loled'o, Ohio, a corporation of Ohio r Ii-Application November 29, i957,'seria1 No. 699,716

4 Claims: (c1; 313-1424 This invention relates to.- electrical spark discharge devices and more specifically to spark plugs incorporating 2,914,693 j. Patented Nov. 24,1959

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. matter. This is particularly. true in connection with very stablemeans for isolating the voltage source from the firing gap of the spark plug while the voltage'builds up to a predetermined amount as well as making a high frequency voltage with respect to the voltage applied to the firing gap of the spark plug out of the conventional ignition coil, This application-is a continuation, in part,

- of our application Serial N0.6S2,597, filed April 12,

The invention jcomp rehends a spark plug including a very consistent auxiliary spark gap located within the insulator in circuit with the spark plug-firinggap 'for controlling the electrical discharge of the latter until. the

firing or secondary voltage of .the ignition system has reached a predeterrnincd Potential. 7 The invention contemplates a spark plug including a sparkintensifier of extremely stablexcharacteristics for isolating ,the voltage; source oi an ignition system while the voltage builds up tojthe predetermined amount from the firing gap -of the spark; plug,;thereby .insuring the electrical discharge notwithstanding the fact that the firing gap of the plug is fouled or shunted by a comparatively lower resistance across the-electrodes by carbon deposits or other deleterious matter., 7 t i The invention comprises a spark plug provided with positioned within the insulator and, inseries with the firing gap of the spark plug, whereby the electrical dis- Q charge of the firing gap of the spark :plug is consistently secured, althoughthe spark plugmay befouled by carbon 'depositor other foreign. or deleterious matter.

overhead valve engines having comparatively high compression ratios wherein the firing gap of the spark plug is not isolated from the voltage source, as in suchcases the condition of the firing gap is one of the main controlling factors in the voltage build-up, and thereby the fouling or the shunting of the ining gap of the spark plug prevents the building up of the voltage to a proper value for obtaining a reliable spark. v

1 his one of the principal objects of the invention to overcome and cure .the failures and drawbacks hereinbefore enumerated by the utilization of a spark plug having a spark intensifier which performs the dual function ofnisolating the voltage source from the firing gap of function acts to build a reservoir or store energyin: the

distributed capacity of the coil, circuit components and wiring harness, and then discharge this stored energy very quickly and at high frequency across the gap of the intensifiers andthe firing gap of the spark plugs ir respective of the presence of a comparatively low resistance path'shunting 'the firing gaps.

Another-object of the invention is to provide a spark plug having a very consistent auxiliary gap incorporating an electrically floating conducting means supported bya dielectric body whereby the electrical field, due to the application'of voltage to its spaced electrodes of the auxiliary gap, causes rapid ionization furnishing free electrons radiating into said gap to thereby produce an 4.0 an extremelystable auxiliary gap: vented to, the atmosphere electrical discharge at consistent andpredictablevoltage,

whereby-not only the spark intensifer has a lowjmpnlse ratio but the firing gap of the spark plug has practically notimelagp'w T Another object of the present inventionis to provide an 'extremelyistablespark intensifier integrally formed in a spark plug whereby the voltage required to produce an electrical discharge across the intensifier and a fouled spark plug gap will be more consistent and thus lower thangthe voltage required wherein conventional intensifiers areused with'sparkplugs. r

intensifier provided. with an electricalfloatirig conduct- 7 ing member arranged. to;.,b1idge the gap between -the i electrodes without; direct connection therewith and sepa rated therefromlby a thinpartition having a dielectric constant higher than air.

According t qthe foregoingsumrnary ofthe invention indicating the general nature and substance, its main ignition systems. s

The conventional spark plugs now in 'use haverbeen entirely unsatisfactory. for prolonged applications in elec trical circuits. ofigni-tion .SYSlZGIIlS for internal combustion engines diie tofthe fact-that the spark plugbecornes fouled r i T s P b'gq me h nt y om ara ive y o r; resistance due to" carbon deposits or other deleterious Another 'objectof this invention is to provide a spark plug having a veryconsistent auxiliary spark gap in which a conducting metallic band is carried on the'outside of a memberfhaving a section of minimum thickness consistent with; its insulatings'trength and which has a dielectric constant highenthan air contacting the electrodes,- and'wherein said conducting band is dimensioned to extend the length of the gap separating the electrode overlapping their firing tips, whereby rapid ionization of the space between the, electrode 'is consistently obtained.

.Afurther object of the invention is toprovide'a spark plug having an extremely stable spark gap intensifier as,a component of its nongrounded electrode', the spark intensifier, being of the non-sealed type andhaving its spaced electrodes interconnected by an insulating body of high dielectric constant operable to provide a surface sparking gap, ..thus eliminating objectionable electrode pitting which made-conventional devices ineffective after short operatingperiods.

I Anotherobject of the' invention is to provide a spark" plug having; a spark intensifying means provided with apreionizing: electrode whichis" solely capacitively coupled to the main arcing electrodes in a wireless, non-inductive," "and; resistantless manner; wherebythe electrical dis-f charges across the gap ofthe spark intensifier are secured at a break-down voltage offcomparatively' low value which F is predictable and consistentix Another object of the-inventionis to provide a spark plug incorporating a ;composite electrode which includes anon-sealed auxiliary spark gap having a preionizing electrode which is only capacitively coupled and structurally associated with each of the arcing electrodes solely by electrical insulating material defining the sparking chamber and which provides spacer means for the preionizing electrode, whereby 'arfcin'g will not occur between either-of the arcing and preionizing electrode as the latter is positioned outside of the sparking area.

l" further object of theinvention is to provide a spark plug incorporating an integrally-formed sparkintensifier ofutmost simplicity which broadly comprises three components; first, spaced electrodes having their discharge or vulnerable surfaces made of high melting point metals or of high erosion-resistant conducting'materialswithout sharp edges; second, a body having a dielectric constant atleast higher than air and of a very thin cross-section consistent with its insulating qualities intervening between the electrodes and in contact therewith to form, in eifect, a surface sparking gap; and,'third, and last coniponent, a conducting Tielectric'allyfloatingid member spacedor separated from the electrodes, by said dielectric body and dimensioned to over extendor bridge the length projecting from its lower end and constituting the firing tip 25 terminating in close proximity to the end of-the coacting firing electrode 26 carried by the lower portion of the shell 10, thereby forming the'firing gap 27 of the spark plug. The metallic stem 24 is provided at its upper end with an enlarged portion or head 28 providing of the surface sparking gap; r. In carrying the present in-';

vention to practice, as shown in;the embodiment herein disclosed, and consistent with economical manufacture, the dielectric body constituting the second component also performs the function of a housing or main support forthe'other components of the spark gap. 1

Other objects and advantages ofithisinventionrelating to the arrangement, operation and function {of the related elements of the structure, to various details ofvconstruction, to combinations of parts andito economies of manufacture, will berapparent to those skilled in mean upon consideration of, thefollowing descriptionand appended claims, reference beinghad to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts 'in the severalviews. 7

Referring to the drawings: c I v Fig. I shows a cross-sectional view of a sparlc plug constructed in accordance with the principles "of the invention in association with a conventional ignition system;

Fig. II is an, enlargedcross-sectional'view' on an enlarged scale of the spark intensifier shown in Fig. I.

The present invention. may be incorporated i'n any suitable typeof ignitionjsystems and devices for producing electrical discharges to ignite combustiblemixture's andfor practical application of its principles, thesame is illustratedin the drawings as embodied in spark plugs for use with; an ignition system for internal combustion engines. However, it is tobe understood that the invention is not limited in its application to the particular form shown but that it is contemplated that the principles of the invention may be used whenever thesame may be found tobe applicable. i j

Referring to the drawings, and particularly to Fig. I, the embodiment of the inventionthereinillustrated -by way of example shows an ignition system including a spark pluglcomprising a hollow'baseor a tubular metallic shell 10 provided at its lower end with an outer threaded section12 and having an outer polygonally-shaped upp'er section 13' for removably mounting the sparkplug in the cylinder block of an internal combustion engine, not

shpwn. The interior surface of the tubular shell hasfareduced lower portion having an inclined annular ledge 14 providing a seat for a sealing ga'sket 15 adapted to be pressed into engagement "with a shoulder 16 of the central enlarged. portion 17 ,of ,the insulator member'18 whereby; the latter is: retained in seale'd relation by spinningthe upper ledge 'or lip 19 of the shell "IO against a CdlfllPI'QSSlblQ ring 20 forced thereby into engagement with the uppershoulder 21 of'theiinsula'torr V In theconstruction shown, to-insurea gas-tight relation between the insulator member-"IS-and the shell- 10 throughout the, heat operating range of the-sparkplug, the shell 10 is formed with afreducedportion a mechanical interlock with the lower shoulder 29 of the insulating bore, which, by suitable sealing means, forms of the'glass sealing body 30. 'The upper end 32 of the pigtail 31 serves asconnector or terminal means for the lower end 34 of the helical spring member 35 freely mounted in the enlarged section 36 of the insulator bore,

The spring 35 is arranged as circuit conducting means to urge the spark intensifier of the invention or auxiliary spark g'apin engagement-With the planarbottom surface.39iof the top hollow metallic section 38 of the composite electrodeofthe spark plug. "The section 38 has threaded engagement with the inner walls of-the enlarged portion 36 of the bore of the insulator, which section provides an elongated chamber on the portion of the insulatorlocated outside of the-she11. Thus the hollow member 38 performs. the dual' function of terminal post for. the: ungrounded; composite electrode and air vent -means. for the elongated section 36 ofthe bore of the insulator. 7 v

The'terminal post 38 of" the spark plug ungrounded electrode is in circuit through the conductor41 to a. high tension terminal of aconventional eight cylinder engine distributor, which is shown in circuit with the rotor member 43,- in turn, connected by lead/45 to the high voltage potential source provided by the secondary winding 46 of an ignition'coil, 'The secondary winding has its other end interconn'ectedwith the endj47 of the primarywindby suitable connections, including switching means 49, with a terminal of a primary sour'ce'of potentialsuch as the storage battery 50 which has its other terminal grounded as atSl to provide a cornn ion'return for the flow of current thereto.- Thefother'" end52 of the primary winding 48 is connected to make and break contacts 5354, the latter grounded as zit 1 56. suitable condenser 57 isconnectedlacrdssthe contacts 53 54, in the conventional manner. The contacts are actuated in tim'ed relation with the engine byj means .of a timing cam 58, which'r'otates' in synchronism with the rotor 43 of the distributor42 by a suitable mechanical, connection shown diagrammatically by dotted lines 59. The scparation'of contacts 53--54"by the earn 5s will cause the interruption. of the current energizing primary winding 48 of the ignition coil andcause theji build up of voltage or firing potential provided by thesecondary winding 46 of the ignition coil to the sparkplug terminal 38. to produce a jump' spark orelectrical dischargefacross the spark intensifier 40 and the firing gap 27 of the spark plug when' gten'ti'al source from the firing' gap of the spark plugwhile the vhltage'bnilds up to a predetermined amount as well as making out of the conventional ignition coil a high frequency source for the voltage that is applied to proditce the jump spark across the firing gap of the spark P 8- c In the embodiment of the invention illustrated, the isolating means which perform the functions before enumerated are in the form of a spark intensifier 40 which broadly includes three components: first, spaced electrodes; second, a body having a high dielectric constant,

at least higher than air, of a very thin cross-section consistent with its insulating quality intervening between the electrodes in contact therewithto form, in effect, a surface sparking gap; and the third and last component, a

current-conducting member spaced or separated from the electrodes by said dielectric body and dimensioned to over extend or bridge the length of said surface spark-' ing gap. In the embodiment of the invention, and as particularly shown in Fig. H, the dielectric body constituting the second component performs two functions; first, as means for decreasing and making consistent the break-down potential required to produce a rapid jump spark across the electrodes and; second, as a support and housing for the other components of the spark intensifier. As particularly shown in Fig. II, the numeral 60 designates a rigid perforated shell or hollow housing having an axial bore centrally located forming an openended tubular enclosure of comparatively thin wall section.

According to the principles of the invention, the housing 60 is made of a material having a dielectric constant at least higher than air and of suitable insulating characteristics to provide a surface or a spacer of minimum thin cross-section intervening between the discharge surfaces of the spaced electrodes.

In carrying the invention to practice, it has been found advantageous to make or form the housing from Suitable ceramic insulating materials, including porcelain whose dielectric constant is considerably higher than air, so that the housing walls are of a minimum cross-section consistent with its insulating qualities; The housing 60 is dimensioned and arranged to support the electrodes 62 and 63 by direct engagement therewith and maintain them apart in fixed position within its axial bore by having a close fit therewith, so that accurate spacing or 'a non-conducting gap of predetermined length is provided. In this embodiment of the invention, the inner surface of the tubular housing 60, and particularly the thin section thereof intervening between the spaced electrodes 62 and 63, operates to form, by intercommunication therewith, a surface sparking gap 61 bridging, in etfect, the non-conducting gap.

Each of the electrodes 62 and 63 is, for ease of manufacture, shown as a duplicate composite structure which, in each case, is pierced at its central portion forming respectively tubular sections 64 and 65. These tubular sections have, at their respective ends, enlarged heads 66 and 67 dimensioned to co-extend and be in alignment with the outer periphery of the tubular housing 60, forming thereby external terminals or connecting plates 69 and 70 for the spaced electrodes. The inner end of the respective tubular sections 64 and 65 are capped by ring-like or annular members 73 and 74 which constitute the other component of the electrode structure and may be termed as its vulnerable end or discharge surface. The tubular sections 64 and 65 of the electrodes 62 and63 are dimensioned to provide a relatively large mass and are preferably made of a base metal or material having good thermal and electrical conductivity not readily oxidizable by electrical discharges.

The vulnerable components 73 and 74 of the composite electrodes 62 and 63 are fixed or carried in direct electrical contact with the ends of the corresponding tubular sections 64 and 65 by having their rear surfaces brazed or welded thereto, and are shaped and di- 6 mensioned so that their surfaces are in intimate contact with the bore of the housing 60.

The annular members 73 and 74 are preferably formed and arranged, so that their discharge faces are uniplanar and rounded off at their outer periphery, as at 76 and 77 respectively, thus avoiding sharp edges or square corners adjacent to the surface gap 61, thus providing co-planar' flat sections spaced adjacent to each other in substantially parallel relation and have their ends adjacent to the central bore rounded off as at 78 and 79 respectively. The vulnerable sections 73 and 74 of the composite electrode structures are preferably made of good erosion-resistant, conducting materials, or of metals having a high melting point. In carrying the invention to practice, it has been found highly advantageous to form each one of the members 73 and 74 of either tungsten, molybdenum, tantalum, or alloys of such metals. However, it is contemplated that other materials having the characteristics before mentioned may be used.

In the form of the invention disclosed, the means to enhance the rapid ionization of the space between the electrodes for decreasing the time lag of the electrical discharge, as well as controlling and stabilizing the breakdown voltage of the intensifier spark gap, are shown in the form of an electrically floating metallic band 81 surrounding or embracing the electrodes but not physically connected to either. The band 81 in the form shown is coaxial with the electrodes and is separated therefrom by being supported by the housing 60 by having direct engagement with its outer surface 82. The band 81 is preferably made of ahomogeneous conducting substance which is illustrated in the form of a flat metallic ring surrounding the electrodes and being dimensioned, so that its length is somewhat greater than the length of the space separating the electrodes, so that the outer ends 84 and of the band 81 extend beyond a slight distance and thereby overlap a portion of the area of members 73 and 74, as can be seen by a perusal of Fig. H.

The conducting member 81, which, in accordance with the principles of the invention in the form shown, depicts the means to reduce the impulse ratio of'the intensifier spark gap and makes possible a fairly low and consistent potential to cause an electrical discharge is symmetrically placed to bridge the surface gap 61 with its outer ends 84 and 85 properly spaced from the en larged sections 66 and 67 of the electrode structure so that flash-over will not occur or precede the electrical discharge between the discharge surfaces 83 and 84. In carrying the invention into practice, it has been found that the space separating the outer surfaces 84 and 85 of the conducting band with respect to the co-adjacent enlarged sections 66 and 67 of the electrodes should be at least more than one-half of the length of the space separating the discharge surfaces 73 and 74, in order to avoid flash-overs therebetween. It has been found by experience, based on comparative tests, that the coaxial separation or radial spacing of the electrical floating body 81 with respect to the electrode significantly affects its function as a controlling factor in reducing the impulse ratio of the spark gap and the consistency of its break-down voltage. In view of this fact, the walls of the housing 60 should be of a minimum cross section consistent with the strength, as well as the insulating characteristics, of the dielectric material from which the same is made.

The length of the dielectric tubular section forming the housing 60 should be correlated with respect to the dimension of the gap 61 and the length of member 81, so that flash-overs between the conducting member 81 and the electrode terminals 69 and 70 will not occur or precede the jump spark across the discharge surfaces 73 and 74 ofthe spark intensifier 40. The conductor body 81 in this form of the invention is preferably produced by spraying or depositing upon the external surface 82 a non-insulating substance to provide a substantially uniform and homogeneous layer of metal or other current-conducting material.

Consistent with economical manufacture, it has been found that depositing a layer of silver in solution upon the external surface 82 of the tubular section of the di-' electric support 60, and thereafter bonding or fusing the same thereto by the application of heat, produces a very effective electric floating metallic member at low costin very close proximity to the electrodes having intimate contact with the outer surface 82 of the housing 69.

Comparative tests indicate that, while maximumeffectiveness is obtained by providing the electrical floating member of the invention totally encirclingv the electrodes, the stability of the gap is not materially impaired when such electrical floating member is circumferentially reduced to 180 degrees. However, it has been determined that further circumferential reduction tends to decrease its effectiveness and thereby its regulating function as a stabilizing and reduction factor for the break-down voltage of the gap. Moreover, it has been found that reduction of the length of the electrical floating member has a tendency to increase the break-down potential for a given gap spacing when such reduction in length does not provide a satisfactory bridging of the gap.

It should be noted that the actual dimensions of the component elements of the embodiment of the invention illustrated in Fig. 11 have been materially exaggerated for sake of clarity, being approximately five times the actual dimensions of the device.

It is to be understood that the above detailed description of the present inventionis intended to disclose an embodiment thereof to those skilled in the art, but that the invention is not to be construed as limited in its application to the details of construction and arrangement ofparts illustrated in the accompanying drawings, since the invention is cap-able of being practiced and carried out in various Ways without departing from the spirit of the invention. The language used in the specification relating to the operation and function of the elements of the invention is employed for purposes of description and not of limitation, and it is not intended to limit the scope of the following claims beyond the requirement of the prior art.

What is claimed:

1. A spark plug comprising a metallic shell, an insulator having a portion mounted in sealed relation within said shell, a central bore transversing said'insulator, a composite main electrode located in said bore, a metallic member sealed to said bore forming the lower component of said composite electrode, said metallic member having one end projecting from the lower end of said insulator, a second primary electrode carried by said shell in spaced relation with the end of said member forming thereby the firing gap of the spark plug, the upper component of said main electrode formed by a pierced conducting member projecting at the upper end of said bore for subjecting the other components of the main electrode to the atmosphere, pierced secondary electrodes having their discharge faces spaced apart to provide a predetermined sparking space subjected to the atmosphere forming thereby an auxiliary spark gap in series with the firing gap of the spark plug, a tubular insulating member having a high dielectric constant directly contacting the outer surfaces of the discharge faces of the secondary electrodes to change thereby the predetermined sparking space into a surface sparking gap, and a current-conducting member carried by the outer surface of said tubular insulating member in a non-conductive relation to the secondary electrodes, constituting thereby an electrically floating conducting member in respect thereto, said current-conducting member having a length dimensioned and arranged to bridge in a nonconductive relation the said surface sparking gap.

2. A spark plug comprising a metallic shell, an insulator having a portion mounted in sealed relation within said' shell and its upper portion projecting therefrom, a central bore transversing said insulator forming an elongated chamber on the upper portion of said insulator, a composite main electrode located in said bore, a metallic stem sealed to said bore forming the lower component of said composite electrode, said metallic stem having one end projecting from the lower end of said insulator, a second primary electrode carried by said shell in spaced relation with the end of said stem forming thereby the firing gap of the spark plug, the upper component of said main electrode formed by a conducting member closing the upper end of said elongated chamber, said conducting member pierced for subjecting the said elongated chamber to the atmosphere, perforated secondary electrodes having uniplanar discharge faces spaced apart to provide a predetermined sparking space subjected to the atmosphere forming in said elongated chamber an auxiliary spark gap in series with the firing gap ofthe sparkplug, a tubular insulating member having a high dielectric constant directly contacting the outer periphery of the discharge faces of the secondary electrodes to change thereby the predetermined sparking space into a surface sparking gap, and a current-conducting band carried by the outer surface of said tubular insulating member in a non-conductive relation to the secondary electrodes, constituting thereby an electrically floating conducting band in respect thereto, said current-conducting band dimensioned and arranged to bridge and encircle in a non-conductive relation the said surface sparking gap.

3. A spark plug comprising a metallic shell, an insulator having a portion mounted in sealed relation within said shell, a central bore transversing said insulator, a composite main electrode located in said bore, a metallic member sealed to said bore forming the lower component of said composite electrode, said metallic member having one end projecting from the lower end of said insulator, asecond primary electrode carried by said shell in spaced relation with the end of said member forming thereby the firing gap of the spark plug, the upper component of said main electrode formed by a perforated conducting member projecting at the upper end of said bore for subjecting the other components of the main electrode'to the atmosphere, perforated secondary electrodes having co-planar discharge faces spaced apart to provide a predetermined air sparking space subjected to the atmosphere forming thereby an auxiliary spark gap in series with the firing gap of the spark plug, a tubular ceramic member having a high dielectric constant having direct contact with the outer peripheries of the discharge faces'of the secondary electrodes to change thereby the predetermined air sparking space into a surface sparking gap, and a current-conducting member bonded to the external surface of said tubular ceramic member in a non-conductive relation to the secondary electrodes to thereby provide an electrically floating conducting member, said current-conducting member having a length dimensioned and arranged to bridge in a nonconductive relation the said surface sparking gap.

4. In a spark plug in combination, an insulator formed with a longitudinal bore, a main composite electrode comprising a plurality of components located within the bore of said insulator, the lower component of said composite electrode formed by a metallic section sealing the bore of said insulator with its end projecting therefrom, the upper component of said composite electrode formed by a hollow metallic member for subjecting the bore of said insulator to the atmosphere, secondary perforated electrodes having uniplanar discharge faces spaced apart in axial alignment to define a predetermined air sparking space subjected to atmosphere forming a sparking gap in series relation to the upper and lower sections of said composite electrode, a tubular member of ceramic insulating material having a dieler/ tric constant higher than air directly contacting the outer peripheries of said uniplanar discharge faces to change the said predetermined air sparking 'space into a surface sparking gap, and a current-conducting member posi- I with respect to the main and secondary electrodes.

References Cited in the file of this patent UNITED STATES PATENTS Skinner Nov. 10,

Trova July 12,

Hutchinson July 18, Donaldson Sept. 19,

Lee Apr. 12,

. Kasarjian Feb. 4,

Palmer Feb. 28, Schwartzwalder Apr. 25,

Booth May 22,

Snell Sept. 3, Twells Sept. 17,

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