US2955222A

US2955222A - Center electrode structure for spark plugs and process for making the same

Info

Publication number: US2955222A
Application number: US822596A
Authority: US
Inventors: Boesch Otto
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1958-06-25
Filing date: 1959-06-24
Publication date: 1960-10-04
Anticipated expiration: 1977-10-04

Description

Qct. 4, 1950 o. BEESCH 2,955,222

CENTER ELECTRODE STRUCTURE FOR SPARK PLUGS v AND PROCESS FOR MAKING THE SAME Filed June 24, 1959 FIG. 1

mwggfl II MEN- its? 2,955,222 Patented Get. 4, 1960 ice CENTER ELECTRODE STRUCTURE FOR SPARK PLUGS AND PROCESS FOR MAKING THE SAME Otto Boesch, Stuttgart-Zulfenhausen, Germany, assignor to Robert Bosch G.m.b.H., Stuttgart, Germany Filed June 24, 1959, Ser. No. 822,596 Claims priority, application Germany June 25, 1958 Claims. (Cl. 313-141) The present invention relates to spark plugs.

More particularly, the present invention relates to that part of a spark plug which forms the lower end section of a center electrode of the spark plug.

It has already been proposed to extrude a pair of blocks of different metals into such a lower end section of a center electrode in such a way that one of the blocks forms an envelope in which a shank formed from the other block is embedded. However, considerable difiiculty and expense is involved in joining to such a structure the sparking point which is made of a metal such as platinum, osmium or tungsten.

One object of the present invention is to provide a special billet with which a sparking point assembled in such a way as to be properly connected to the remainder of the structure as a result of the extrusion so that it becomes unnecessary to assemble such a sparking point with the lower end section of the center electrode after extrusion of this lower end section.

It is also an object of the present invention to provide a process according to which a billet is extruded into the lower end section of a center electrode of a spark plug in such a way that a sparking point is permanently connected with this section of the center electrode.

It is also an object of the invention to extrude a structure which requires practically no further working before it is assembled into the spark plug.

With the above objects in view, the present invention includes a center electrode structure of a spark plug, this center electrode structure including an outer envelope of one metal in which a shank of a core member of a different metal is embedded. A sparking point extends in part into an end wall of the envelope, and the material of this end wall presses against and surrounds the sparking point to fix the latter to the envelope. The assembly of the above elements, namely, the outer envelope, the core member and the sparking point, is extruded in one step according to the present invention, from a billet made up of a pair of blocks of different metals located closely adjacent to each other and adapted to be extruded into a structure wherein one of, the blocks forms the above envelope and the other of the blocks forms the above core member whose shank is embedded in the envelope and, in accordance with the present invention, that block of the billet which subsequently forms the envelope has fixedly connected thereto, before the extrusion takes place a sparking point which is positioned in such a way that at the end of the extrusion, part of the sparking point is embeddedin an end wall of the envelope.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims- The invention itself, however, both as to its construction and its method of'operation, together with additional objects and advantages thereof, will be best understood from the following description top end portion surrounding the lower portion of the head'- of specific embodiments when read in connection with the accompanying drawings, in which:

Fig. 1 is a fragmentary sectional diagrammatic view of an extruding die and ram used to extrude the billet structure illustrated in Fig. 1 into the structure illustrated in Fig. 2; V

Fig. 2 is a partly sectional elevational view of an unfinished lower end section ofa center electrode of a spark plug, this lower end section being extruded from the structure illustrated in Fig. 1;

Fig. 3 shows the finished lower end section of the center electrode which is formed from the structure of Fig. 2;

Fig. 4 is a top plan view of the structure of Fig. 3;

Fig. 5 is a fragmentary sectional illustration of another embodiment of an extruding die and ram and billet assembly extruded thereby; and

Fig. 6 shows the structure resulting from the extrusion of the billet of Fig. 5 with the press of Fig. 5.

Referring now to Fig. 1, the structure illustrated therein includes the die 1 formed with a receiving chamber 2 for receiving the billet assembly illustrated in Fig. 1. The chamber 2 communicates with the discharge opening 3 of the die 1, this discharge opening 3 communicating in turn with a bore portion 4 of an enlarged diameter as compared to the discharge opening 3. The chamber 2 is joined to the opening 3 by a frustoconical bore portion 5 whose angle of inclination 0: is approximately 30 in the illustrated example.

The billet assembly of Fig. 1 includes a sparking point 6 made of a noble metal such as platinum. It will be noted that the sparking point 6 has an enlarged frustoconical head and is received in an opening of the lower block 7 of the illustrated billet assembly. This opening extends through the block 7 and has an enlarged frustoconical configuration adjacent the upper face of the block 7 to receive the enlarged head of the point 6. The point 6 has an inner shank portion pressed into the opening of the block 7 and an outer shank portion extending freely beyond the block 7 before extrusion takes place, as illustrated in Fig. 1. The block 7' may be made of nickel and after the point 6 is assembled therewith, a layer of silver solder 8 is located between and fused with the blocks 7 and 9 to form the billet assembly illustrated in Fig. 1. The upper block 9 of Fig. 1 maybe made of copper, and the illustrated billet assembly is inserted as a unit into the receiving chamber 2'of the die 1.

With the above-described billet thus located in the die 1, the ram 11- of the extrusion press, which is provided with the conical end face 10, is axially pressed into the chamber 2 so as to extr-ude the billet through the bore portion 5 and the discharge opening 3' until the structure has the configuration illustrated in- Fig. 2. When the billet of Fig. 1 has been extruded into the structure shown in Fig. 2, the extrusion is stopped, the ram 11 is retracted, and the extruded article is removed from the die in an-upward direction, as viewed in Fig. 1, opposite to the direction of movement of the ram 11 during extrusion, so that in this way the extruded article of Fig. 2 is separated from the die 1.

As is shown at the right, sectional portion of Fig. 2, the platinum sparking point 6 has'been changed only to a slight degree, while the block 7 has been formed into the envelope 7 in which the elongated shank of the coremember 9 is embedded. The core member 9 has an enlarged head end, and the envelope 7 has an enlarged end of the core member 9 which is located next to the shank thereof. As a result of this construction, the envelope 7 extends upwardly beyond the shank of the core member 9 so that it is the upper part of the. envelope 7 which rests on a mating shoulder of the electrical nonconductive insulating body of the spark plug when the structure of Fig. 2 is assembled therewith. This construction is of considerable advantage in that the corrosion action of the combustion gases can extend during operation only along the shank up to the enlarged head of the core member, so that the envelope protects the entire core member in this way against such corrosion.

' The structure of Fig. 2 may be finished to form the structure shown in Fig. 3. Since the upper part 12 of the structure of Fig. 2 is composed of copper, it is easy to work. Thus, this upper part 12 may be placed between three jaws similar to the jaws of a chuck and these jaws are simultaneously moved toward each other along radial lines extending from the center of 'a circle along which the jaws are located so that by pressing the upper part of the assembly in this way, it is formed into the connecting portion 13 shown in Figs. 3 and 4, this electrical connecting portion 13 being: made up of three fins'spaced from each other by 120 as shown most clearly in Fig. 4. The excess material of the head portion 12 illustrated in Fig. 2 is turned off to form the collar 14 illustrated in Fig. 3. Also, at the lower end of the assembly in the vicinity of the sparkingpoint 6, the envelope 7 is turned oif as indicated at 15 in Fig. 3 so that when the structure of Fig. 3 is'assembled with the rest of the spark plug structure, a heat-insulating air gap will be The noble metal which forms the sparking point 6 or 6' neednot necessarily be platinum and can be, for example, alloys of osmium or tungsten. If it is desired to avoid the relatively high pressure required by the ram 11', inasmuch as this ram does not include a forwardly projecting end similar to the end 10 of the ram 11 which first engages the core-forming block only at a central portion thereof, it is possible to reverse the ram structure by providing the bottom end of the ram 11 with fins similar to the fins 13 so as to form in'the upper portion of the extruded structure a Y-shaped opening, so that with this construction the electrical connecting member. is formed by a member having a Y-shaped opening'rather than fins. With such a construction, the ram need not be applied with as high a pressure as is required by the structure of Fig. 5.

The envelope 7 or 7 can be made of nickel, chromium or alloys thereof. 7

In the past, in order to save costs, a sparking point of a noble metal has been joined to an element such as the envelope 7 as by being welded thereto. However, because of the small dimensions of the parts, they are difficult to handle and the manufacturing costs are relatively I high. Furthermore, the welding of a sparking point of formed around this lower portion of the assembly of Fig. 3 between the latter and the outer ceramic insulating body of the spark plug. The embodiment of the invention which is illustrated in Fig. 5 shows several simplifications as compared to the above-described structure, and these simplifications result in a substantial reduction in the manufacturing costs. The platinum sparking point 6' is considerably shorter than the sparking point 6 and the opening of the nickel billet block 7 which receives point fi'extends only partly through the block 7'. The sparking point 6' is fixed to the billet block 7 by being Welded or soldered thereto before the extrusion takes place. Also, the billet assembly of Fig. 5 diifers from that of Fig. 1 in that the copper block 9. is directly welded to the nickel block 7', and the billet assembly 6', 7' and 9 is inserted as a unit into the receiving chamber 2' of the die 1. The fusing of the billet blocks 7 and 9' to each other can easily be carried out in a protective gas atmosphere composed of a gas or gases which are inert with respect to the materials being fused to each other at the fusing temperature.

Also, it will be noted from a comparison of the die 1' of Fig. 5 with the die 1 of Fig. 1 that the ratio of the diameter of the receiving chamber 2' to the discharge opening 3' is smaller than in the embodiment of Fig. l, and also, it will be seen that the extruding ram 11 is formed with an opening 10 which has the configuration of the connecting portion 13' illustrated in Fig. 6. This connecting portion 13' is substantially identical with the connecting portion 13 of Fig. 3 so that with the structure of Figs. 5 and 6, the Y-shaped connecting portion 13 is formed during the extrusion and does not require an additional step and structure. The frustoconical bore portion 5' of the die 1' has an inclination different from the bore portion 5 of Fig. 1 because of the diiferent relationship between sizes of the openings and components, of the billet assembly. The billet assembly of Fig. 5 will be extruded directly into the article shown in Fig. 6 except that there will be along the outer periphery of the collar 14 at the end of the latter directed toward the extruding ram 11' a burr which is easily removed. Upon removal of this burr, the structure shown in Fig. 6 is provided and may be assembled directly with the remaining structure of the spark plug, so that practically no working beyond the extrusion itself is required with the embodiment of Fig. 5.

Of course, some of the simplifications of Fig. 5 can b incorporated into the other embodiment, of the invention.

noble metal to the envelope results in the unavoidable disadvantage of poor head conductivity. With the abovedescribed process and billet structure, the resulting structure shown in Figs. 24 and 6 overcomes all of the above disadvantages and the sparking point is joined to the assembly in an extremely simple and effective manner guaranteeing that during the cold extrusion of the billet assembly not only will the lower center electrode structure be formed but, in addition, the sparking point will be simultaneously securely anchored to the assembly with the lower free end portion of the sparking point 6 or 6' exposed in the manner illustrated in Figs. 3 and 6.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of spark plugs differing from the types described above.

While the invention has been illustrated and described as embodied in center electrodes of spark plugs, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by V gated metallic core member having an elongated shank;

an elongated metallic tubular envelope of a metal different from said core member, said shank being embedded in said envelope and said envelope having an end wall located beyond a free end of said shank and formed with an opening which opens onto an end face of said envelope which is directed away from the free end of said shank; and a sparking point of a noble metal having an inner shank portion located in said opening and at least part of the material of said end wall surrounding and pressing against said inner shank portion of said sparking point for fixing the latter to said envelope, said sparking point having an outer shank portion extended freely beyond said end wall of said envelope.

2. For use in a spark plug, in combination, an elongated metallic core member having an elongated shank; an elongated metallic tubular envelope of a metal different from said core member, said shank being embedded in said envelope and said envelope having an end wall located beyond a free end of said shank and formed with an opening which opens onto an end face of said envelope which is directed away from the free end of said shank; and a sparking point of a noble metal having an inner shank portion located in said opening and at least part of the material of said end wall surrounding and pressing against said inner shank portion of said sparking point for fixing the latter to said envelope, said sparking point having an outer shank portion extended freely beyond said end wall of said envelope, said opening of said end wall of said envelope extending only partly through said end wall.

3. For use in a spark plug, in combination, an elongated metallic tubular envelope of a metal different from said core member, said shank being embedded in said envelope and said envelope having an end wall located beyond a free end of said shank and formed with an opening which opens onto an end face of said envelope which is directed away from the free end of said shank; and a sparking point of a noble metal having an inner shank portion located in said opening and at leastpart of the material of said end wall surrounding and pressing against said inner shank portion of said sparking point for fixing the latter to said envelope, said sparking point having an outer shank portion extended freely beyond said end wall of said envelope, said opening of said end wall of said envelope extending only partly through said end wall and said sparking point having an enlarged head end embedded in said end wall of said envelope.

4. For use in a spark plug, in combination, an elongated metallic core member having an elongated shank; an elongated metallic tubular envelope of a metal different from said core member, said shank being embedded in said envelope and said envelope having an end wall located beyond a free end of said shank and formed with an opening which opens onto an end face of said envelope which is directed away from the free end of said shank; and a sparking point of a noble metal having an inner shank portion located in said opening and at least part of the material of said end wall surrounding and pressing against said inner shank portion of said sparking point for fixing the latter to said envelope, said sparking point having an outer shank portion extended freely beyond said end wall of said envelope, said opening extending through said end wall of said envelope.

5. For use in a spark plug, in combination, an elongated metallic core member having an elongated shank; an

elongated metallic tubular envelope of a metal difierent from said core member, said shank being embedded in said envelope and said envelope having an end wall 1c!- cated beyond a free end of said shank and formed with an opening which opens onto an end face of said envelope which is directed away from the free end of said shank; and a sparking point of a noble metal having an inner shank portion located in said opening and at least part of the material of said end wall surrounding and pressing against said inner shank portion of said sparking point for fixing the latter to said envelope, said sparking point having an outer shank portion extended freely beyond said end wall of said envelope, said opening extending through said end wall of said envelope and said sparking point having a head end pressed between said free end of said shank of said core member and said end wall of said envelope.

6. A billet adapted to be extruded into an elongated body which forms at least part of a center electrode of a spark plug, said billet comprising in combination, a pair of blocks of different metals, respectively, located closely adjacent to each other, said blocks being adapted to be extruded simultaneously into an elongated body wherein one of the blocks forms a tubular envelope and the other of the blocks forms a core at least part of which is embedded in the envelope, said one block being formed with an opening extending at least partly into said one block from an end face thereof which is distant from and directed away fnom said other block; and a sparking point carried by said one block in said opening thereof and having an elongated free end portion extending beyond said end face of said one block, so that said free end portion of said sparking point will be exposed after said one block is extruded into said envelope.

7. A billet as recited in claim 6 and wherein said blocks are fixed directly to each other.

8. A billet as recited in claim 6 and wherein a layer of solder is located between and united with said blocks.

9. A billet as recited in claim 6 and wherein said opening of said one block extends entirely through the latter and has an enlarged portion at a face of said one block which is opposed to said end face thereof and directed toward said other block, said sparking point having an enlarged head end located in said enlarged portion of said opening.

10. A billet as recited in claim '6 and wherein said opening extends only partly through said one block and said sparking point having a head end in said opening fixed to said one block.

References Cited in the file of this patent UNITED STATES PATENTS