US2906908A - Spark plug - Google Patents

Description

M. MALLORY s'ept. 29, 1959 SPARK PLUG Filed April 19, 1957 JNVENTOR MAR/0N Mano/w 5mm 015m, fw/51H66# ATTORNEY-5' United States Patent hice SPARK PLUG Marion Mallory, Detroit, Mich., assignor to The Mallory Research Company, Detroit, Mich.

Application April 19, 1957, Serial No. 653,858

7 Claims. (Cl. 313-1144) This invention relates to spark plugs for use in internal combustion engines.

Objects of the invention are to provide a spark plug wherein,

(l) The insulator body has extensive pressure engagement with an annular metallic element carried by the shell, thereby promoting rapid heat transfer between the insulator body and shell,

(2) The center electrode has contact along its entire length with cement carried within the insulator body, thereby promoting rapid heat transfer between the electrode and insulator body,

(3) The joint between the center electrode and insulator body is sealed along the entire electrode length so as to provide maximum protection against leakage,

(4) The joint between the insulator body and shell is sealed by means of an annular wedged in metallic element in such manner that the sealing action and heat transfer are increased at high operating pressures and temperatures, thereby-eliminating the need for preheating of the plug during its assembly,

(5) The plug design is such that the plug can be manufactured by low cost processes while still maintaining close control of the plug operating characteristics,

(6) The nature of the plug manufacturing process gives such close control over the plug operating characteristics as to permit formation of plugs in different heat ranges by varying a single characteristic of the plug insulator body, thereby enabling the manufacture of an entire line or" plugs with the same machinery.

Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this speciiication wherein like reference characters designate corresponding parts in the several views.

ln the drawings:

Fig. l is a vertical sectional view through one embodiment ofthe invention,

Fig. 2 is a View of the Fig. l embodiment with its component parts in a partially assembled condition, and

Fig. 3 shows the lowerportion of an insulator body which can be utilized interchangeably with the Fig. l insulator body.

Before explaining the present invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other Vembodiments and of being practiced or carried out in various ways. Also,

it is to be understood that the phraseology or terminology employed herein is for *the purpose of description and not of limitation.

In Fig. l there isshown a spark plug 10 comprising an annular metallic shell 12 provided with the usual ground terminal 16 and external threads 14 for securement of the plug on the engine cylinder head (not shown). Shell 12 is internally contoured to provide a lower bore 18, `outwardly extending shoulder 20, and upper bore 22.

2,966,908 Patented Sept. 29, 1959 Bore 22 has an inward upward taper of about three degrees with respect to the shell axis.

iositioned within shell 12 is a porcelain insulator body 23 which includes a lower body portion 24, a shoulderforming portion 26, and an upper body portion 28. Body portion 28 has an inward upward taper of about ten degrees with respect to the shell axis. The extreme upper end oi body 23 is provided with ribs 29 which increase the insulator surface over which a charge must travel in order to short circuit around terminal 16.

ln order to secure insulator body 23 within shell 12 there is provided a ring 30 of aluminum. This ring could be formed of copper or other soft metal, it being essential that its material be relatively soft and deformable so as not to crack the porcelain insulator body during assembly or use in the engine.

Initially ring 30 is formed with an annular wall which begins to taper at a point about one third of the way down from its upper end as shown in Fig. 2. Prior to assembly of ring 30 into shell 12 insulator body 23 is positioned on a soft copper gasket 32 as shown in Fig. 2. Shell 12 is xedly positioned in a fixture (not shown) and vertical pressure is applied downwardly on the upper edge of ring 30 to force said ring down into the space between body portion 28 and tapering bore 22. A suitable huid-actuated press having an annular pressure pad (not shown) may be employed to provide the pressure on ring 3l). As the lower end of ring 30 strikes body portion 28 it is cammed outwardly toward its Fig. l wedged in position between surfaces 2S and 22. Part of the mechanical force applied to ring 30 is transmitted to gasket 32 so as to deform it to its Fig. 1 inclined position against the surface of shoulder 20.

In the Fig. l position insulator body 23 is rigidly positioned within shell 12 without any tendency to shift axially during operation. At high engine temperatures (during the tiring stroke) metallic ring 30 tends to expand so as to more tightly pressure against walls 22 and 28. As a result the heat within the insulator body can be rapidly dissipated to shell 12. Additionally, the joint along the surface of body portion 28 is insured of an extremely tight and extensive seal during the tiring stroke. The utilization of ring 3b to retain the insulator body in the shell (in lieu of the conventional spinning over of the shells upper edge) eliminates the need for preheating of the plug during its assembly, such preheating being necessary in the conventional construction in order to give the insulator body a tight fit during service in the engine. Ring 30 is of soft material so that the insulator body does not crack in service.

The center electrode within insulator body 28 takes the form of a cylindrical rod 34 which is preferably formed of nickel alloy in order that it can be secured onto the lower end of steel terminal 36 by a low cost clinching operation. Terminal 36 is provided with a bore 38 which receives the upper end of rod 34, after which the terminal and rod are clinched at 40. The electrode and terminal are secured together before their assembly into the insulator body.

Prior to insertion of the electrode-terminal assembly into the insulator body the internal bores 42, 44 and 46 in the insulator body are iilled with two cements. Bore 42 is slightly greater in diameter than rod 34, and bore 44 is about one tenth inch greater in diameter than rod 34. Bore 46 is threaded to mesh with threads 48 formed on terminal 36. Bores 42 and 44 are filled with a relatively porous, high viscosity cement 50 to the level of imaginary line 52. The walls of threaded bore 46 are then sprayed with a second cement 54 which is of relatively low viscosity.

Cement 5) is compounded from 70% Sauereisen filler No. 32 and 30% Sauer-eisen binder No. 32, both the filler and binder `being standard items manufactured by the Sauereisen Cement Company of Pittsburgh, Pennsyl- Vaniat The ratio of ller to binder may however be varied from the specified ratio, especially 'when mixed or used at high or lo'w 'room temperatures, and when allowed to stand ior extended periods 'after mixing.

`Ceir'nr'i't `54 is compounded from kaolin 'and silicate of so'da solution A"('Type N, manufactured by Philadelphia Quartz 'Company and distributed Vby Ecclestone Chemical Company of Detroit, Michigan). The 'kaolin and silicate of soda are compounded by adding one voiurnetric part silicate :of vsoda to three volumetric parts 'loosely packed kaolin (i.e., as it comes from the .package with no packin'g or 'tam'pingy The proportion of kaolin to silicate Yof soda may however be varied within limits and stiil obtain satisfactory cement "characteristics When cement '50 is poured into Vbores 4Z and 44 its high viscosity, together (with the 'small diameter of bore 42 (about one sixteenth inch), prevents anyV appreciable liquid flow out of 'the llower end of bore 42. Downward linsertion of rod 34 vinto bores 42 and 44 'expels some of cement Sil out of the lower end o'f bore '42; however, enough of the vcement remains lto completely yline vthe walls of bores 42 and 44.

Additionally, rod 34 cooperates with lcement 5G10 'seal bo're V42. and-put the cement in bore 44 under pressure; as a result there are lno large void spots within :the cement. Insertion of terminal 36 into bore 46 is accompanied by a `slight expelling'of `cement 54 upwardly out of bore-46past laluminum gasket et?. y

After threads V48 are meshed with threads46 '(as 'shown in Fig. 1) the terminal-electrode Aassembly is Vplaced in an oven Vat elevated temperatures (in excess of 100 F.) fors'everal hours to cure cements 50 and 54.

In service, cements 50 and 54 'provide a seal along the entire length of the electrode-terminal assembly, as well as an `extensive'heat path for dissipation of electrode Y heat into the insulator-body.

Cements 50 and 54 are purposely made of Ydifferent materials because of their different locations within the insulator body. -Cement 50 is a relatively porous material, which yin the -liquid state is of high Viscosity Yin order that it can be retained under pressure in bores 42 and 44 during insertion -of rod 34 into the insulator body. The porosity of cement 5t) allows its filler particles to moveror'shift slightly in service during electrode temperature increase without cracking the porcelain insulator body. A`Gement 54 is a light material having relatively small size filler particles. The rclearance spaces between threads 46 and 48 are relatively small but the character of cement 54 is such that it does not crack the po'rcelain insulator body during high temperature service conditions. A cement having large size filler particles would not be practicable for use in threaded bore 46. v

fIt will vbe noted `that the lower body portion 24 of insulator 23 includes-a-conical section 62 and a-cylindrical section`64. The upper end of section 62 has adiameter corresponding with the internal diameter -of gasket 32 so as `to automatically seat body 24 in a central position priorlto pressing in of ring 30.

The length of section 64 determines rate of plug cooling and Vhence the operating temperature of the'plug. -Thelonger the-length of section 64 thehigher'will'be the plugoperating temperature. The Fig insulatorbody has Aa lower operating temperature thanV the Fig.`

-1 insulator bodyrand can be employed interchangeably therewith. This interchangeability is due to the highv v rate and closeco'ntr'ol of'theheattransfer action'through andcements-St), 54. Each plug'therefore-has aprecise fheat transfer characteristic; asfaresult variation 11i-the length of -se'ctio'n 64fcan be-eniployed to Vprovide a complete line of plug ,heat ranges.

*It will lbeV noted that the lower end portion of rod 34 extendsJalrel-atively short distance beyond'thjelower'lrimt of insulator body 23. In practice this short length of exposure of the electrode (which may vary between .020 and .045 inch) causes the electrode to be out of the hot engine gases which cause burning, carboning and electrode deterioration.

It will be noted that there are more ribs 29 on body 2.3 than can usually beY accommodated on an insulator body. The large number ofV ribs .29 is made possible because of the short length of ring 30 and the fact that upper end portion 65 of shellrllZ is not turned radially inward to clamp the insulator body in place as in conventional constructions. Ribs 29 can be extended down into the space within end portion 65 so as to provide increased resistance *to 'current dash over from terminal 36 to shell 12.

I claim:

l. A spark plug comprising an annularrmetallic shell internally contoured to providea first lowe'r bore, a shoulder extending outwardly from the upper end of said bore, and a second 4bore extending upwardly from 'said shoulder, said second bore tapering upwardly and inwardly; 'an insulator body extending downwardly into the shell and having an upwardly and inwardly tapering portion located within 'the upwardly and inwardly tapering bore; an annular body ofrsoft metal wedged between the tapering portion and the Jtapering bore; an electrode extending downwardly lthrough the insulator body; and a second electrode carried yby the Elower lend yof the shell.

2. A spark plug comprising an annular metallic shell 'internally contoured to provide -t-wo aligned -bores of different diameters and a shoulder therebetween, the larger of said bores tapering `upwardly and inwardly; an annular gasket seated on 'the -shoulder; lan insulator body having a rst relatively's'ma'll diameter Vvbody portion and a second relatively large diameter body portion the juncture therebetween vdening an annular 'abutment -surface; :said insulator body extending through the shell with the small diameter portion positioned within the small diameter bore and with the large diameter portion 'positioned within the large 'diameter bore, said abutment surface being seatedbn the gasket; the large diameter portion tapering upwardly and -inwardly '-from the abutment surface;v a '-'ring of softV metal *wedged between the tapering body tportion and :the tapering bore; lan electrodeextending through thet insulator fbody; and a second electrode carried -by -the shell. Y

3. In a spark plug an linsulator body lhaving a lower 'relatively small bore; an intermediate largerfbore, and an 'upper lthreaded bore; a `terminal threaded into said upper bore; an lectrode-carried by said terminal and extending'downwardly through the-tirst two 'boi-es, said electrode having aV diameter'slightly less than that of the lower bore; a rst porous cement of relatively high viscosity lining the wall surfaces 'of the lower 4and intermediate bores; and a second cement of low viscosity lining the wallsurfaces Vof'the'th'readed bore.

4. 'Ihe combination of claim V3 Ywherei'nthe terminal is formed with a borein'itslower.end,'said electrodebeing formed yof nickel 'alloy and being extended into the terminal bore; the bore-forming Vwall of the terminal being in a radially squeezed condition so -as tosecure theelectro'de"ontothefterminaL i. Y

" 5. The combination of claim '3 'whereinjthes'e'cond Vcement is comprised'of kaolin and silicateof'soda.

6. TheA combination of claim Y3 wherein the 'electrode ture therebetween defining an annular abutment surface; said upper body portion tapering upwardly and inwardly from the annular abutment surface; said lower body portion including a conical section tapering from Vthe abutment surface and a cylindrical section extending downwardly from the lower limit of the conical section; said insulator body extending into the shell with its abutment surface seated on the gasket and with its upper body located within the tapering bore; an annular body of soft metal positioned between the upper body portion and the tapering bore; a terminal carried at the upper end of the insulator body; an electrode extending downwardly from the terminal through the insulator body; cements between the electrode-terminal assembly and insulator body; and a second electrode carried by the lower end of the shell; the claimed arrangements permitting rapid heat transfer between the first electrode, insulator body and shell.

References Cited in the file of this patent UNITED STATES PATENTS

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