US2717438A - Spark plug with auxiliary gap - Google Patents

Description

K. scHwARTzwALDl-:R ETAL 2,717,438

Sept. 13, 1955 SPARK PLUG WITH AUXILIARY GAP Original Filed March 17, 1945 :inventors 9 f W w z h rn w. Mw

,sr M MM KK m Zl/I I attorney United States Patent@ Mich.; lassignonbto sGeneraLMotorsv fCorporation, De-

txoit,r lvlich.,- ,ancorporatidnaof. Delaware Oi'igaiiapplication-Marchin 1945;' Serinl'No.' 583,364.' Divided fand this applichtin\AugustA-'25,' 1949, Serial No. 115,039 ff (c1. zafzsiz) This invention has to do with spark plugshavingan auxiliary=sparkI f gap incorporated-Liri fthe' center electrode.

'Iltis-application is-iiled-.ilnderRille'l47 'as a divisional.

application-Lof'Srial-No'. 583',364,-le"d-March 17, 1945, now Patent No.' 2,505 ,150#issued Aprill25,` 1950.'

ableit to'functioniefectivelydong'after-it would otherwise ihave'ebeen e shortcircuitedfby fouling, -that' is by the accumulationflo carbonaand 'otherfconducting combustion chamber A-products -ontthe lfiring end ofthe plug formingV a conducting path between theelectrode's; This Vactionis increased/byplacingthe auxiliary gap `as close as possi-V ble'fto-Lthesparkigapiofthe plug`because the distributedVv capacityj'of"thefportion-ofthe center electrode between' th'twogaps istherebyireduced-'to a minimum Aproducing f afsteepjwave-fr'ontatthe'sparkgapgso'that there is insuicient time for Aleakageof'fcurrent through'the path produced by fouling topreventthe -spark =from jumpingthe gap.

An object rofatheepresentinvention -isf-toprovide an auxiliary gap of. durable constructionthatmay be readily incorporated in the center electrode of a spark plug and willfopevrateA ati substantially constant voltage throughthe lifel'of the plugt- Another 'object ofthe/invention fis-the provision of a simple and practical center electrode construction embodying an auxiliary spark gap.

In the drawings:

Figure 1 is a vertical sectional View through one form of spark plug embodying my invention.

Figure 2 is a vertical sectional view through a modified form of spark plug embodying my invention.

In Figure 1, indicates the lower part of the metal shell of the spark plug having secured to its lower end the side electrodes indicated at 12. Within the shell is the insulator 14, preferably of aluminum oxide composition. The insulator is held in its seat in the shell by any suitable means such as by annular C-shaped spring 16, metal washer 18 and the upper part 20 of the shell which is threaded in the lower part 10 and may also be welded or brazed thereto. tween the shoulders of the insulator 14 and the shell 10 and C-shaped spring 16 to distribute the pressure evenly on the insulator. The upper portion 20 of the shell is provided with the usual sleeve 22 of insulating material held in place by any suitable means. Insulator 14 is provided with a central bore 24 having an enlarged upper end and a reduced lower end. Fitted within the reduced lower end is the lower electrode section 26 which may be made of metal, such as nickel, which is resistant to heat as well as to spark erosion. This portion of the electrode has an enlarged upper end which seats on the shoulder formed at the junction of the enlarged and reduced portions of the insulator bore 24, and is preferably of hollow construction with the center lled with metal such as copper, indicated at 28, having good heat conductivity.

Above the lower electrode section is the conducting glass seal 30; above that a resistance element 32; and

Suitable gaskets are interposed bev 2,717,438 g Patented Sept.13, 1,955

above the resistance.` element `a second conducting p glass seal 34 orr which"isiseated;the disca421 ofthe lower ele'c-` trode 44 ofthe' auxiliary gap;v An'additional 'glass seal 31"'- engages` and 'grips vthe -lower threaded Ylor serratedgend 'of the upper electrode ele`u1entf38.V Y Y The auxiliary 'spark gap assemblyj 36 'is of' simple con-V struction consisting ofr a sleeve' y41)*"of insulatingfmateriahi, preferably steatte, althouglraluminumj 'oxide'for otherV cef; rarnic compositions" maybeemployed. St'eatite vis .preferf able' because it 'maybeY readily.' cut 'to' the,.'desired'.`size`. Theersleeve shouldjhave' a'.roughj "surfa'ce to .reducethe possibility 'of 'shortfcircuiting by rdeposition of the -metal sputtered fromthe electrode." ,Eachend of'tliecylfinder., is closed by adisc `42l 1avingsecured, centrallylth'ereto acylindricalelectrodeisection The dises 42preferably, consist of heat resistant conducting material; such as Vcom-l mercial nickel, and the electrodes 44arekpreferablylmade" of 'tungsten because of. Aits excellent resistance to' heat, spark'erosion and oxidation. V'Ilietungstencontacts may., be secured tother nickel discs bywcopper br`azing0r..the like. Other Amaterials "suitable for use,l as electrode'saal!" thoughinefe'rior to.tungsten.are'platinum, platinum tung?, sten alloy, `nickel andl other allo'ysA commonly; used "fon spark fplugeleetrode's. Copper-will" be found .`satisfac tory T where `lower fabricating andf'operating ,temperatures are involved.'` y Y l The-.auxiliary v'spark 'gap ,should be.of 'suchlength that. the voltage across itis substantially the same as thatfacross., the gap of the plug. Asthe `pressure anthesauxili'ary gap is` .atmospheric ,and Imuch lower than inl.the combustion chamber the auxiliary gap Idistance should be muchgreat-- er than the sparkg'glP-.- I

The conductinglgla'ss sealsl. and 34 fand 'the resistancev element. 32 "may be; of 'the constructio'n described and 'claimed .in` the p rfior Aapplication of.,'McDougaLlA Schwartzwalde'r and Rulk,.Serial Nol-,488',114,le'd May., 24, 219431 Thus `the seals' 30 .and'34 may beniadekoflfznA fused mixture.` ofi55fparts, powderedy copper, 45. Pyrex or borosilicateI glass together with 3 `parts of a suitable binder such'as Dritex, a hydrogenated cottonseed oil.

The resistor 32 may be made of a mixture of 62.4% borosilicate glass (Pyrex cullet), 25.2% fluorspar (CaFn), 7.8% magnesium borosilicate glass and 4.6% Thermax carbon, a form of carbon black.

The glass Seal 37 above the spark gap may consist of Pyrex glass but the following composition is preferred:

It will be noted that this seal contains no organic binder corresponding to the Dritex used in the conducting glass seals 30 and 34. It has been found that when a binder is present in the glass seal compositions during the fusing of the glass in the insulator bore a carbon film is deposited on the insulating sleeve 40 of the spark gap, which lowers the insulation resistance of the auxiliary spark gap assembly and may cause the gap to.be inoperative. However, when the binder is omitted the powdered material is diicult to handle in the small amounts required. Consequently instead of omitting a binder entirely from the composition of the conducting glass seals 30 and 34, the binder is employed to form the powdered material into pellets which are subsequently sintered, preferably in a hydrogen atmosphere, at from 1500 to 1700 F. for from fifteen minutes to one hour. The resulting pellets are substantially free from the binder and may be readily handled in manufacture.

In assembling the electrode in the insulator the lower electrode element 28 is inserted in the bore followed by the powdered or pelleted materials constituting the lower conducting glass seal 30; then bythe pulverized or pelleted material forming the resistor 32 and then by the pulverized or pelleted material forming the upper conducting glass seal 34. It has been found best to use either all powdered material or all pelleted material for the parts 30-32-34 as the combination of powdered and pelleted material does not produce the desired nal structure. Thereafter the spark gap assembly, the glass seal 37 and the upper electrode section 38 are inserted and the assembly is then heated to a suiiicient temperature to soften the glass of the seals and resistance element whereupon the upper electrode section 38 is pressed down to cause it to seat on the upper disc 42 and make a tight assembly. On solidication the conducting glass seals 30 and 34 form an air-tight union with the Walls of the bore in the insulator and grip the other parts with which they make Contact.

An important feature of the invention is the character of the glass seal 37. It has been found that when a gastight seal is used at this location the voltage across the auxiliary spark gap increases as the plug is used because of disappearance of the air from the gap. The preferred glass composition of the seal 37 produces a crazed or finely cracked glass which, while securely united to the insulator and the cooperating parts, nevertheless permits seepage of air into 4the auxiliary gap. With this construction the voltage drop across the auxiliary gap has remained substantially constant throughout the life of the plug.

In the modification shown in Figure 2 the construction of the shell and the manner of mounting the insulator in the shell is substantially the same as that previously described. The electrode, however, consists of a platinum tip ,50, the upper end of which is slightly enlarged and rests on a shoulder provided in the bottom of the bore 52 in the insulator. The section 54 of the electrode consists of silver cast in place. Above the silver is the glass seal 56 which may be of the copper glass lcomposition described with the Dritex eliminated by baking the glass pellets. If desired, a resistance may be incorporated in the glass seal as disclosed in Figure l. upper section of the electrode, the lower end of which rests on the upper disc of the auxiliary gap assembly indicated at 60. The electrode section 58 may be corrugated or grooved as in the preceding form to better interlock with the glass of the seal 57 which is of the same composition as the seal 37 of Figure l.

Various modifications will occur to those skilled in thev art. Thus, for example, compressed powdered talc lcould be used in place of the glass seals, suitable means being provided to hold it under compression. The upper seal instead of consisting of crazed glass permitting theentrance of air could be provided with a vent for the same purpose.

Various other modifications will occur to those skilled in the art.

We claim: Y

The method of making spark plugs having an auxiliary gap therein, said method comprising the steps of preparing a ired ceramic insulator with a central bore, arranging therein in the order named, a lower electrode section, a powdered mixture of glass and electrically conducting heat resistant material, an auxiliary gap assembly comprising a lower electrode, an upper electrode and-aY tubular insulator interposed therebetween, a quantity of powdered glass adapted after softening and cooling to form a crazed or cracked structure pervious to air and an upper electrode section, heating the assembly to soften the glass, applying pressure axially to said upper electrode section to cause it to seat in electrically circuit engaging relationship on the upper electrode of the auxiliary gap while simultaneously causing the otherparts of the Velectrode to form a tight assembly and thereafter cooling the assembly to cause the glass to solidify in situ withthe glass surrounding said upper electrode section crazing to admit air to said auxiliary gap assembly.

References Cited in the file of this patent UNITED STATES PATENTS -2,371,2l1 Barrington Mar. 13, 1945 2,453,048 Tognola et al Nov. 2, 1948 58 Vindicatesv the

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