US1228767A - Spark-plug and method of manufacturing the same. - Google Patents

Description

F: MfFURBER.

SPARK PLUG AND METHOD OF MANUFACTURlNG THE SAME.

APPUCATION FILED MAR. 17. 1917- 1,228,767 Patented June 1917.

i N VEN TUE WWW UNITED STATES PATENT OFFICE.

FREDERICK M. FURBER, OF REVERE, MASS.ACHUSETTS.

SPARK-PLUG AND METHOD OF MANUFACTURING THE SAME.

Specification of Letters Patent.

Patented June 5, 1917.

Application filed March 17, 1917. Serial No. 155,463.

. provements in Spark-Plugs and Methods of Manufacturing the Same, of which the following description, in connection with the accompanying drawings, is a. specification, like reference characters on the drawings indicating like parts in the several figures.

This invention relates to spark plugs and to methods of manufacturing spark plugs. The exceedingly keen competition which has arisen in recent years in the spark plug industry has made the adoption of economical constructions and methods of manufac ture of these devices a practical necessity to the maintenance of a successful business in this line. At the same time the users of spark plugs have become more exacting in their requirements and are demanding a spark plug of a much sturdier and more substantial construction than has heretofore been required. The trade is also demanding a spark plug that is very reliable and is substantially gas tight under operating conditions; and these changes in the demands of the trade have, of course, complicated the problems presented to the spark plug manufacturers. It will readily be appreciated by those skilled in this art that the chief manufacturing difiiculty resides in the assembling of the insulator in the body or shell of the plug. This difficulty arises primarily from the fact that the insulators are relatively fragile and that they vary greatly in dimensions. Most of-these insulators are made of porcelain which, of course, warps and becomes distorted in the baking operations,

thus producing extraordinary variations in I dimensions which require the use of gaskets or similar means to accommodate these variations and prevent the application of excessive pressure to relatively small areas of the insulator. Even then these variations render it difiicult to apply the pressure necessary to produce a gas tight joint between the insulators and the shells without breaking the insulators.

The present invention has for its general object to devise a spark plug that will sat isfy the requirements of the trade and at the same time to devise a plug construction and a method of manufacturing it which will solvethe problems presented to the manufacturer. Stated more specifically, the inventlon aims to devise a sturdy, substantial and reliable spark plug which can be economically manufactured and which will be so constructed that much of the skill and exactness required in manufacturing spark plug constructions heretofore proposed will be eliminated.

The invention is particularly concerned with the mounting of the insulator in the shell or body of the plug.

The invention will be readily understood from the following description, reference being made to the accompanying drawings, in which:

Figure l is a view in perspective of a spark plug embodying the invention;

Fig. 2 is a vertical cross sectional view of the plug shown in Fig. 1-;

Fig. 3 is a side elevation of a part of the spark plug, showing a step in the process of manufacture Fig. 4 is a fragmentary cross sectional view, on a large scale, of a part of the spark plug shown in Figs. 1 and 2;

Fig. 5 is a cross sectional view, partly in elevation, showing the spark plug and one of the tools that operates on it;

Fig. 6 is a View, partly in vertical cross section and partly in side elevation, showing the apparatus which distorts the shell to clamp the insulator therein; and

Fig. 7 is a cross sectional View of a part of a modified form of plug.

The plug shown comprises a shell or body 2, which may be made out of cold rolled stock of hexagonal cross section, the lower part of this shell or body being turned down to form a shank which is screw threaded to adapt it to be secured in an engine cylinder. The shell is drilled to form a bore therethrough and is counterbored from its outer end, that is, the end which projects out of the engine cylinder when the plug is in use, to form an internal shoulder or seat 4. An insulator 6 is positioned in the bore of the shell 2 and is provided with a circumferential enlargement 7, the ends of which form upper and lower shoulders 8 and 9, respectively. The shoulder 4 in the shell forms a seat for the lower shoulder 9 of the insulator 6, a gasket 10 being interposed between this seat and the shoulder.

The insulator is held in the shell by means of an annular flange 12 formed integrally with the shell 2 at its outer end and turned inwardly over the upper shoulder 8 of the insulator into position to clamp the en largcment 7 of the insulator securely against the seat 4. Preferably a gasket 14 is interposed between the shoulder 8 and the flange 12 to protect the shoulder. It will be noted that the enlargement 7 of the insulator is so much smaller in diameter than the bore of the shell that a lateral clearance is provided between the shell and the peripheral surface of the enlargement 7. The insulator thus is secured in the shell solely by the parts that engage the shoulders 8 and 9.

Accordin to the preferred method of manufacturing the plug, the insulator and shell are made in the usual way but the shell 2 is provided with an annular flange 12 at its outer end, as shown in Fi 6. The gaskets 10 and 14 are then place on the shoulders 9 and 8, respectively, and the shell is inserted in the plug in its normal or operative position. The shell 2 then is supported in an upright position in a die 16, as shown in Fig. 6, and another die or swaging tool is employed to turn the flange 12 inwardly or crimp it over the shoulder 8. It will be noted that while the flange 12 is relatively thin as compared-with the main body of the shell, it is thicker than the flange usually employed in s ark lugs of this general construction. uch anges heretofore have been made very thin so that they could be crimped readily over the upper shoulder of the insulator; and according to the processes heretofore followed in the assembling plugs of this type the flange has been crimped or turned over at a single operation. In some instances the flanges are heated sufficiently to render them relatively plastic so that they can be distorted more readily. In all of these cases, however, difiiculty has been encountered in handlin insulators in which there is an apprecia 1e variation in the height of the enlargement at different points circumferentially thereof. I It will readily be appreciated that if the flange 12 of the insulator were turned in by a bell-shaped die, of the character usually em loyed, or by spinning, and the enlargement were appreclably higher on one side than the other, the high side would be subjected to much greater pressure than the low side; and the probable result would be either to break the insulator or else to leave the flange in such a condition that the plug would not be gas tight on the low side of the insulator.

According to the present invention the flange is turned in, or crimped, in such a manner that it clamps the enlargement of the insulator against the seat 4 with a pressure which is substantially uniform at all points circumferentially thereof.

Referring now to Figs. 3 and 6, it will be seen that the upper die comprises two members 18 arran ed to operate on the flange 12 at diametrica ly opposite points, (using the term points, not in its geometrical sense,

but rather in the sense of designating a relatively small area). The members 18 are both secured pivotally to a yoke 20 and are held in a properly spaced relation to each other by guides 22. These upper die members 18 are reciprocated toward and from the lower die 16 in a direction parallel to the axis of the spark plug. The mechanism by which this movement 1s produced, may comprise a plunger 24 connected to the yoke 20 by-a pivot 26, which is mounted in the yoke and passes through a slot 28 in the lower end of the plunger. A stifi coiled spring 30 surrounds the plunger 24 and bears at one end against the yoke 20 and at its opposite end against a head 32 with which the plunger is provided. A power driven mechanism of some kind may be employed to act through the head 32 to apply pressure to the upper die, and the arrangement just described equalizes this pressure between the two die members 18 which act directly on the flange 12. v

As clearly shown in Figs. 3 and 6, the lower ends of the two die members 18 are shaped to force the part of the flange which they engaged inwardly over the upper shoulder 8. Preferably these flange-engaging parts of the dies are notched to provide tooth-like projections A Fig. 3 with spaces, as B, between them. Conse uently,'when the upper die is forced towar the lower die, these members will force the parts of the flange which they engage inwardly over the shoulder 8 into the crimped or turned-in position in which they are shown in Figs. 1 and 4. When the upper die 18 recedes, the plug is turned or indexed into position for the next downward stroke of the die; and this operation is continued until the points of operation of the upper die have been transferred completely around the flange and the entire flange has been crimped over the upper shoulder of the insulator. It sometimes is preferable to operate twice around the flange in this manner.

It will now be understood that according to this process only asmall part of the flange is distorted at one time and that by operating on the flange at diametrically opposed points and equalizing the pressure applied to these points, a very great pressure can be applied to each point of operation so that the firm clamping of the insulator inthe shell is insured. At the same time, if the enlargement 7 of the insulator is higher on one side than the other, which practically always is the case, the flange is turned over against the upper shoulder at both sides with substantially the same pressure, notwithstanding these variations in height. For the sake of economy in manufacture, it is preferable to perform the crimping operationallows the metal to flow laterally in opposite Y direction from the points at which the greatest distortion of the metal of the flange is taking place and thus avoids the danger of cracking the flange which otherwise Imght prove troublesome in attempting to crimp it while in a cold condition.

This process produces a flange that varies in thickness and also in density at successive points circumferentially of the flange and this construction of the flange is of advantage in stiffening it and enabling it better to resist any tendency to spring back or return toward its original position. This construction, however, is not regarded as absolutely essential in the finished plug provided the flange is made of suflicient thickness and these corrugations may be turned off if desired after the plug has been completed. The variation in density of the flange will still be present, however, as will also the variation in density lengthwise of the flange due to its being turned inwardly.

Preferably the gaskets 10 and 1 1 conslst simply of washers made of some soft metal, such as copper. This material protects the shoulders of the insulator from IlIlJIlIY which they might otherwise sustain by contact with the harder metal of which the shell is made, and at the same time it does not yield sufficiently to relieve the firm clamping pressure which the flange 12 exerts on the upper shoulder 8. It is found in practice that satisfactory results are obtained by applying to the upper die a pressure of approximately 2,000 lbs, in performing the crimping operation. This pressure is equalized between the two die members 18 so that substantially 1,000 lbs. are applied to each member at each operative stroke of the plunger. It is obvious that the upper die member could be arranged to operate simultaneously at more than two points on the flange, if desired, but such an arrangement would require the application of considerable morepressure to the die mechanism inorder apply the same amount of pressureto ca point at which the distortion or crimping of the flange is taking place. Accordingly, I prefer to arrange the apparatus as shown. But whether the crimping action takes place simultaneously at two or more points, it is preferable to have these points spaced apart at substantially uniform distances circumferentially of the flange, and to equalize the pressure used so that the pressure applied at jitrouble, this difliculty can be obviated by each point will be substantially the same as that applied at any other point. This arrangement is of material advantage in pre venting the breakage of the insulators in casethe enlargement of the shoulder is appreciably higher on one side than on the other and also in producing a gas tight joint between the insulator and the shell.

In making spark plugs of this general type according to the methods heretofore practised, the use of a relatively soft gasket between the lower shoulder 9 and the seat 4: has been relied upon to produce a gas tight oint because it was found practically impossible to make a gas tight joint at the upper end of the enlargement 7 and still use the fir'mer gasket which seemed advantageous at this point. The present method,

however, produces a gas tight joint at the upper end of the enlargement 7 notwithstanding substantial variations in the height of this enlargement at this point circumferential ly thereof. This result is produced by crlmping only relatively small parts of the flange 12 at a time and equalizing the pressure between the points at which the crlmping operation is taking place, so that when this operation is completed, the flange is shaped to conform the upper gasket to the contour of the upper shoulder 8 and maintains a substantially uniform pressure on sa1d gasket at all points circumferentially thereof notwithstanding the variations in the height of said enlargement. If desired the flange 12 may be grooved internally, as indicated at 38, Fig. 7 to provide annular grooves and ribs on its inner surface which enable this part better to grip the upper gasket 14 during the crimpmg operation, and to exert a better holding action on the gasket thereafter. This construction however is not usually necessary.

As above stated, a lateral clearance is provided between the bore of the shell and the peripheral surface of the enlargement 7 so that, while there may be a contact between these surfaces at one or more points, there is no possibility of the shell exerting sufficient pressure on the insulator laterally thereof to crush the insulator.

' The construction of the plug herein shown and described is such that any ordinary and reasonable variations in the dimensions of the parts of which it is made up do not interfere with the production of a satisfac- -.'itory.iplug. It will be evident from an in spection. of Figs. 2 and 6 that any reasonable varia"on in the depth of the counter-bore of thejplug, in the thickness of the gaskets 1O andfl l, and in the height of the enlargementsg7 will not be sufiicient to prevent the flange from being crimped into clamping relationship to the insulator as above dejscribed. If, however, due to unusual conditions these variations seem likely to cause making the flange 12 long enough to take the reducing action when the flange has been out down to substantially a predetermined height above the shoulder 8 and above the gasket 14.

It is obvious that practically all the operations in the manufacture of the shell and in the mounting of the insulator in the shell can be performed by automatic machinery and that much of the exactness heretofore required in the manufacture of these parts is eliminated by this invention. The cost of manufacture of a plug according to this construction and by this method is materially reduced. Furthermore it has been found from actual practice that this invention solves the difficulties heretofore experienced in producing a gas tlght oint between the insulators and the shells, even when the insulators are very badly Warped,

and that an unusually small percentage of the insulators are broken in the process of assembling the plugs.

\Vhat is claimed as new is:

1. A spark plug comprising a shell hav-.

' ing a bore formed therethrough, an insulator positioned in said bore and having a circumferential enlargement with shoulders at the opposite ends of said enlargement, a seat in said shell supporting one of said shoulders, and a corrugated flange at the outer end of said shell turned inwardly over the other shoulder of said insulator and clamping the insulator in the shell.

2. A spark plug comprising a shell having a bore formed therethrough, an insulator positioned in said bore and having a circumferential enlargement with shoulders at the opposite ends of said enlargement, a seat in said shell supporting one of said shoulders, and a flange at the outer end of said shell turned inwardly over the other shoulder of said insulator to secure the inextending ribs in its outer face and annular ribs in its inner face. 4. A spark plug comprising a shell havtor positioned in said bore and havin a.-

circumferential enlargement with shoul ers at the opposite ends of said enlargement, a. seat in said shell supporting one of said shoulders, and a flange at the outer end of said shell turned inwardly over the other shoulder of said insulator to secure the insulator in the shell, successive portions of "said flange both circumferentially and longitudinally thereof being of different densities.

6. A spark plug comprising a shell having a bore formed therethrough, an insula- .tor positioned in said bore and having a circumferential enlargement with shoulders at the opposite ends of said enlargement, a seat in said shell supporting one of said shoulders, and a flange at the outer end of said shell turned inwardly over the other shoulder of said insulator to secure the insulator in the shell, said flange varying substantially in thickness at successive points circumferentially thereof.

7. A spark plug comprising a shell having a bore formed therethrough, an insulator positioned in said bore and having a circumferential enlargement with shoulders at the opposite ends of said enlargement, a seat in said shell supporting one of said shoulders, the distance between said shoulders varying appreciably at different points circumferentlally of said enlargement, and an annular flange at the outer end of said shell turned inwardly over the other shoulder and exerting a substantially uniform pressure on said enlargement at all points cireumferentially thereof.

8, A spark plug comprising a shell having a bore formed therethrough, an insulator positioned in said bore and having a circumferential enlargement with upper and .lower shoulders, respectively, at the oppo- -s1te ends of said enlargement, a seat in said shell supporting the lower of said shoulders, and a flange at the outer end of said shell, integral with the shell, and turned inwardly over the upper shoulder, said enlargement varying appreciably in height at different points circumferentially thereof, and said flange being shaped to exert a substantially uniform pressure on said u per shoulder at all points circumferentially thereof and thereby'to clamp said enlarge ment against said seat.

. 9. That improvement in the method of securing an insulator having a circumferential enlargement with upper and lower shoulders, respectively, at the oppositeends of said enlargement, in a spark plug shell having an internal seat for the lower of said shoulders, which consists in forming a flange in the outer end of said. shell, placing said insulator in the shell, and turning said flange inprogressively over the upper shoulder of the insulator into clamping relationship therewith.

10. That improvement in the method of securing an insulator having a circumferential enlargement with upper and lower shoulders, respectively at the opposite ends of said enlargement, in a spark plug shell having an internal seat for the lower of said shoulders, which consist in forming a flan e in the outer end of said shell, placing said insulator in the shell, and acting on a relatively small part only of said flange at a time, and with a substantial predetermined force, to force it inwardly over said upper shoulder into position to clamp said en-' tial enlargement with upper and lower shoulders, respectively, at the opposite ends of said enlargement, in a spark plug shell having an internal seat for the lower of said shoulders, which consists in forming a flange in the outer end of said shell, placing said insulator in the shell, and turning said flange inwardly over said upper shoulder 1n such a manner that the flange will exert substantially a uniform pressure on said upper shoulder at all points circumferentially thereof notwithstanding variations in the height of the enlargement.

' 12. That improvement in the method of securing an insulator having a circumferential enlargement with upper and lower shoulders, respectively, at the opposite ends of said enlargement, in a spark plug shell having an internal seat for the lower of said shoulders, which consists in forming a flange in the outer end of said shell, placing said insulator in the shell, and turning said flange inwardly over said upper shoulder while the flange is at substantially normal temperature in such a manner that the flange will exert substantially a uniform pressure on said upper shoulder at all points circumferentially thereof notwithstanding variationsin the height of the enlargement.

13. That improvement in the method of securing an insulator having a circumferential enlargement with upperand lower shoulders, respectively, at the opposite ends of said enlargement, in a spark plug shell having an internal seat for the lower of said shoulders, which consists in forming a flange above the upper shoulder of the insulator,

and turning said flange inwardly over said upper shoulder in such a manner that the flange will exert substantially a uniform pressure on said upper shoulder at all points 'circumi'erentially thereof. notwithstanding variations in the height of the enlargement. I 14. That improvement in the method of securing an insulator havinga circumferential enlargement with upper and lower shoulders, respectively, at the opposite ends of said enlargement, in a spark plug shell having an internal seat for the lower of said shoulders, which consists in forming said shell with a relatively thin annular flange at its outer end, inserting said insulator in the shell, and turning said flange in over the upper shoulder progressively by operating on a small part only of the flange at a time and allowing part of the metal of the flange to flow laterally'away from each point of operatlon.

' 15. That improvement in the method of securing an insulator having a circumferentlal enlargement with upper and lower shoulders, respectively, at the opposite ends of said enlargement, in a spark plug shell having an internal seat for the lower of said shoulders, whlch consists in forming said shell w1th a relatively thin annular flange at its outer end, inserting said insulator in the' shoulder into clamping relationship therewith 'while the flange is at substantially normal temperature by operating on said flange at points spaced apart at substantially equal distances circumferentially of the flange andapplying substantially the same'pressure to each of said points, and transferring said points of operation around the flange until said crimping operation is completed. 16. That improvement in the'method of securing an insulator having a circumferential enlargement with upper and lower shoulders, respectively, at the opposite ends of said enlargement, in a spark plug shell having an internal seat for the lower of said shoulders, which consists in forming said shell witha relatively thin annular flange at its outer end, inserting said insulator in the shell, and turning said flange over the upper shoulder progressively into clamping relationship therewith by operating on it simultaneously at substantially diametrically opposite points and equalizing the pressure applied tosaid points.

17. A spark plug comprising a shell having a bore formed therethrough, an insulator positioned in said bore and having a circum ferential enlargement with upper and lower shoulders,-respectively, at the opposite ends largement varying appreciably in height atdifl'erent points circumferentially thereof, and a gasket on said upper shoulder, said flange being shaped to conform said gasket to said upper shoulder and to maintain a substantially uniform pressure on said 10 gasket at all points circumferentially thereof notwithstanding said variations inthe height of said enlargement.

In testimony whereof I have signed my name to this specification.

FREDERICK M. F URBER.

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