US1968314A - Spark plug and method of making the same - Google Patents

Description

O. C. ROHDE July 31,1934.

2 Sheets-Sheet 1 Filed Jan. 14, 1933 EQ======== I .v

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July 31, 1934. o. c. ROHDE SPARK PLUG AND METHOD OF MAKING THE SAME Filed Jan. 14, 1933 2 Sheets-Sheet 2 Patented July 31, 1934 UNITED STATESPATENT OFFICE SPARK PLUG AND METHOD OF MAKING THE SAME Otto C. Rohde, Toledo, Ohio, assignor to Champion Spark Plug Company, Toledo, Ohio, a corporation of Delaware Application January 14, 1933, Serial No. 651,781

13 Claims. (Cl. 29-155.51)

This invention relates to a spark plug and a and out, this finish having some insulating propmethod of makingthe same. More particularly erties. The finish may be removed from the it relates to the formation-of a gas-tight joint inner end of the counter bore in bushing 12 between the mica insulation of the spark plug where it is contacted by beveled end 22 of sleeve and the electrode on one side and the shell on 21, and from the shoulder.immediately opposite 60 the other side. Details and minor objects of this point. the invention will appear as the description pro- With the parts thus assembled, they are placed ceeds. in the device shown in Figs. 2' and 4. This com- Inthe accompanying drawings forming a part prises an abutment member 30 supported by a of this specification, Fig. 1 is a sectional view of strong spring 31 upon a support 32. Rods 33 85 an initial assembly in making one form of a extend upward from support 32 and have fasspark plug embodying my invention; tened to their upper end a cross piece 34 which Fig. 2 is a view of assembled mechanism for has therein a socket 35 adapted to receive bushperforming the next step in the making ofthe ing 12. Below socket 35 there is an opening 36 plug after that shown in Fig. 1; to receive the insulation 17. The upper end of 70 Fig. 3 is a longitudinal section of a spark plug abutment has a socket 3'7 adapted to receive in the stage after it has been treated by .the the lower end 16 of the electrode and surroundmechanism in Fig. 2; ing insulation. Bushing 12 is held in socket Fig. 4 is an enlarged section of the plug and y C mp g members 3 fas n d n place by 20 immediately associated mechanism shown in screws 39. Fig. 2; A plunger head 40 has an opening 41 therein Fig. 5 is a longitudinal section of a completed to receive the electrode 14 and sleeve 15. The plug formed in accordance with Figs. 1 to 4'. pp r D t On Of t s pening is e ed at 42 The completed spark plug shown in Fig. 5 ei a p er S e 43 which has in t 25 will be described first. In this view there is lower end a socket "44 to receive the upper end shown the usual shell 10 having the screw threads of electrod 4- Head 0 i e in j s D 11 adapted to be screwed into the cylinder wall eitien up member 43 by a Screw 45 other of an internal combustion engine. Within the ea s- A in 6 is cla ped about ea top of the shell there is threaded a bushing 12 means of a member 47. Y

30 seated upon a gasket 13. The central electrode Cross-head 34 is insulated from other portions 14 has wound about its central portion mica of the mechanism and abutment 30 is preferably sheets 15 forming an insulating sleeve; Beof non-conducting materiaL Cross-head 34 may tween the lower end 16 of the electrode and the be connected to a source of electricity by a terlower end of bushing 12 there is insulation minal at 48, while another terminal is attached 35 formed by mica discs 1'? while a similar series at 45. Thereupon with the parts in position as of mica discs 18 is provided above the bushing shown in Fig. 4, electric current passes from and below the attachment member 19, which has cross-head 34 t r bushing 12 i t lower a groove therein 20 for reception-of a'terminal. end otfiller sleeve 21 and thence through plunger In the making of the plug, the sleeve 15 is head 40. It will be understood that spring 31 is 4o first wound upon electrode 14 and then mica sufliciently strong to-insure proper compression discs 17 are placed in position. Thereafter bushof insulation 1'7 so that the bushing l2 is held in ing 12 is placed around sleeve 15 above the discs properaelation to electrode 14 and sleeve 15.

17 and a filler sleeve 21 is inserted between the Suflicient'current is employed to meltth lower bushing and sleeve 15. In the form shown, filler end of the filler sleeve, first at its lower beveled 45 sleeve 21 has a somewhat reduced lower end 22 end, then progressively valong the thin portion and a slightly thickened upper end 23 which is to shoulder 26, then along the thicker portion to designed to" just fit within the upper bore 24 of upper end 23. Enough pressure is exerted on the bushing 12. Below the upper end, the bore of upper end of filler sleeve 21 toinsure the pressing bushing 12 is .enlarged as at 25. In the form down of its upper end as its lower end melts, and

50 shown, sleeve 21 isthinner above beveledend he curr nt isre that pper end23 re- 22 to shoulder 26 than thereabove to upper end m s hards d ring is p e down 23. A low-manganese steel containing one or preferably un il i is flu wi h Slightly l w two per cent manganese, for example, issuitable the top of he surreuhding'bushing. and forces material for the sleeve. The steel bushing is the molten metal against the bushing'and mica.-

55 preferably given the usual black finish, inside Pressure is continued while the metal sets.

The ring 23 forms a close fit with the top of the surrounding bushing, but preferably does not make good electric contact therewith during its insertion therein, as a good electric contact at this point tends to shunt the circuit around the lower part of the sleeve that isbeing progressively melted. A very slight clearance, especially when aided by a black finish or similar slight coat, is sufiicient to prevent detrimental shunting.

After the pressing operation, the cooling of the heated metal about sleeve 15 further compresses that sleeve so that a thoroughly gastight joint is produced at 50, (see Fig. 3). Since the metal of filler sleeve 21 is seated in the bushing while molten, the fit is so close as to be gastight under ordinary circumstances but, if desired, there is a welded union of the reduced lower end 22 of sleeve 21 with the bushing, as indicated at 51 on Fig. 3. This welded union is not ordinarily necessary to make a gas-tight joint, but may be provided, if desired, for purposes of safety.

Upper ring 23 fits closely around sleeve 15, but

' is not shrunk thereon like the molten metal below, and consequently there is no sharp upper shoulder cutting into the mica. Likewise, the bevel 22 at the bottom not only aids in localizing the initial heat so as to start melting at that point, but also results in less pressure on the mica at this point, so that the inner surface of the filler sleeve is somewhat convex in the finished plug, as shown-in Fig. 3, and provides compression over a considerable length of the mica sleeve without any sharp shoulder at any point that is likely to break or injure the mica.

Since the metal is molten while being fitted into the counter bore of the bushing, it is pressed in every direction by the applied pressure, and conforms exactly to any irregularities in the contbur of the space, even such-slight irregularities as result from the beginning and terminations of the lamina of mica making up sleeve 15. The pressure exerted by ring 23 is sufilcient to insure this accurate fit, but need not approach that necessary to deform solid metal. The slight expansion of the steel during solidification may assist in the close fit which it is found to have within the shell even after cooling to the 'temperature of the shell.

After the parts are thus assembled, as shown in Fig. 3,the insulating members 18 are placed in position after which a washer 52 is placed thereon and upper terminal member 19 is pressed down upon insulating washers. The upper end of the bore in member 19 is flared at 53 and the top of the electrode is upset at 54 so as to rivet the parts in assembled relation. The bushing 12 is then screwed into sleeve 10 to. form the completed plug shown in Fig. 5.

By the above described arrangement it will be seen that there is provided a permanent gastight joint between the insulating member and the surrounding metallic member bywhich the spark plug is mounted.

While one construction has been shown in considerable detail, it will. be understood thatchanges in the details of the method and plug may be ma e within the scope of the appended claims, wher in the term shell is intended to ing a, shell onto a non-vitreous insulating tube surrounding an electrode which consists in exerting pressure upon molten metal in the space between the shell and tube, and maintaining the pressure until the metal solidifies, the solidified metal as it cools shrinking onto the tube.

2. In making a spark plug, the method of sealing a shell onto a non-vitreous insulating sleeve surrounding an electrode, which consists in exerting pressure upon molten metal in the space between the shell and tube, and maintaining the pressure while the metal sets in interlocking engagement with the shell and in intimate contact with the tube, the solidified metal as it cools shrinking onto the tube.

3. In making a spark plug, the method which consists in winding thin mica sheets about an electrode and thereby forming an insulating tube, surrounding the tube with a shell, exerting pressure upon molten metal inthe space between the shell and tube, and maintaining the pressure while the metal sets in intimate contact with the shell and tube, the solidified metal as it cools shrinking onto the tube, thereby pressing the tube against the electrode.

4. In making a spark plug, the method which consists in winding thin sheets of mica around an electrode to form an insulating tube, surrounding the tube with a shell having an undercut counter bore, exerting pressure upon molten metal in the counter bore and maintaining the pressure while the molten metal solidifies in intimate contact with the tube and with the undercut portion of the counter bore, the solidified metal as it cools shrinking onto the tube.

5. In making a spark plug, the method of sealing a shell onto a nonvitreous insulating tube surrounding an electrode, which consists in introducing between the shell and tube a metal sleeve while melting the sleeve progressively, beginning at its inner end, and pressing the molten metal melted end into the space between the shell and tube and thereby forcing the molten metal into close contact with the shell and tube, and solidifying the molten metal .,while it is in such close contact, the metal as it cools shrinking onto the tube. v

7. In making a spark plug, the method which consists inwinding thin mica sheets about an electrode and thereby forming an insulating tube,

surrounding the tube with a shell having a grooved counter bore around the tube, inserting a metal sleeve into said counter bore, melting the inner end of the sleeve progressively while it is being inserted, and continuing to press the unmelt ed outer end of thesleeve into the counter bore while allowing the molten metal to solidify in interlocking engagementwith said groove and in intimate contact with said tube, the solidified metal shrinking onto the tube as it cools, thereby compressing the tube against the electrode.

8. In making a spark plug, the method which I consists in placing a metal shell around a nonvitreous insulating tube surrounding an electrode, introducing a steel sleeve into the space between the shell and tube, forcing the inner end of the sleeve into contact with the shell, passing an electric current through a portion of the shell and through the sleeve and thereby melting the sleeve progressively from its inner end towards its outer end, but leaving the outer end unmelted, pressing the unmelted outer end of the sleeve into said space and thereby bringing the molten metal into intimate contact with the shell and tube, and solidifying and cooling the steel and thereby sealing the shell to the tube and compressing the tube onto the electrode.

9; In making a spark plug, the method which consists in placing a shell around a non-vitreous insulating tube surrounding an electrode, introducing a manganese steel sleeve into the space between the shell and tube, passing an electric current through the sleeve to melt the inner end thereof, and pressing the unmolten outer end of the sleeve against the molten metal and solidifying the molten metal under pressure, the

solidified metal as it cools shrinking onto the tube.

10. In making a spark plug, the method which consists in winding thin sheets of mica around an electrode to form an insulating tube, surrounding the tube with a metal shell having a counter bore aflording a space between the shell and tube, inserting a manganese steel sleeve into the said space, making an electric contact between the shell and inner end of the sleeve and passing an electric current through the shell and sleeve through said contact and thereby melting the inner end of the sleeve, and pressing the molten metal into said space while it solidifies, the solidified metal shrinking onto the tube by cooling.

11. A spark plug comprising a central electrode, a non-vitreous insulating tube surroundin the electrode, a shell surrounding the sleeve, and a metal seal between the shell and tube, said seal being fitted in place while molten and under pressure and thereby exactly fitting all irregularities in contour of the interior of the shell and exterior of the tube, and shrunk onto the tube and pressing the tube into sealing contact with the electrode.

12. A spark plug comprising a central electrode, a mica tube around the electrode, a shell around the tube, and a steel seal, pressed into place while molten, between the shell and tube, and thereby fitting exactly the contour of the interior of the shell and exterior of the tube and being shrunk onto the tube arid pressing it into sealing contact with the electrode. 13. In making a spark plug, the method of sealing a shell onto a non-vitreous insulating tube surtoundingan electrode, which consists in exerting pressure upon molten metal in the space between the shell and tube andmaintaining the pressure until the metal solidifies, said metal when cooling having its degree of shrinkage gradually reduced at its outer end to avoid a sharp shoulder in impingement with the insulating tube.

-' OTIO C. ROHDE.

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