US3452235A - Spark plug having a short tip center electrode - Google Patents

Description

June 24, 1969 w. J. HALLAUER ET AL 3,452,235 SPARK PLUG HAVING A SHORT TIP CEilTER ELECTRODE Filed Aug. 17, 1966 lNVE N TOPS HA1 4/9051? J POM //V ATTORNEYS United States Patent 3,452,235 SPARK PLUG HAVING A SHORT TIP CENTER ELECTRODE William J. Hallauer, Dearborn, and Donald J. Romine,

Taylor, Mich., assignors to Ford Motor Company, Dearborn, Mich., a corporation of Delaware Filed Aug. 17, 1966, Ser. No. 573,017 Int. Cl. F23q 3/00; H01t 13/20, 13/00 US. Cl. 313136 8 Claims ABSTRACT OF THE DISCLOSURE This invention provides a spark plug that uses a wire seated in a short center electrode cup and surrounded by a heat conducting medium to provide a heat conductivity path from the sparkplug tip. The spark plug requires reduced amounts of the expensive metals needed for center electrodes and also is easier and more economical to manufacture.

Prior art spark plugs comprise center electrodes either of one-piece construction or of a center wire surrounded by a cup-shaped member seating in the insulator at or above the plane in which the insulator seats in the shell. An electrode of this length was necessary to provide a heat conductivity path from the tip of the spark plug to the massive portion of the insulator and, subsequently, to the shell and surrounding mediums.

Large amounts of expensive metals and alloys are required in those long electrodes. In addition, production tolerances are difficult to maintain along the length of the electrode and, in many plugs, a vacuum cementing operation between the electrode and the insulator is required to insure good heat conductivity. In some prior art spark plugs, the long center electrode is cast in place, but differences in thermal expansion coefiicients of electrode and insulator necessitate careful control over materials and casting temperatures and thereby deprive such constructions of intended manufacturing and operating advantages.

In the spark plug of this invention, the insulator has a tip portion, a massive portion above the tip portion, and a passage extending through both portions. The electrode comprises an exterior member for resisting electrical discharge erosion that seats in the insulator tip portion. An interior member in intimate heat conducting contact with the exterior member and smaller than the passage extends above the exterior member and into the massive portion of the insulator. A heat conducting composite of metal powder and glass fills the passage between the interior member and the insulator, so that an excellent heat conducting path from the exterior member through the interior member and the composite is provided.

With the exterior member in the shape of a cup, the interior member can be in the form of a wire fitting into the opening of the cup. This construction does not require a seal between the exterior and interior members and increases the heat conducting contact area of the members. A heat conducting medium then fills the space between the wire and the insulator.

Thermal expansion coeflicients of metal-glass composites used as the heat conducting medium can be controlled easily to provide a transition zone maintaining excellent thermal contact with the insulator and the Wire. The composite also can serve as a seal for the center electrode structure or as a nonsealing termination for an integral resistor seal.

A cross section of an aircraft spark plug having the short cup center electrode structure of this invention is shown in the drawing and is described below in detail.

Referring to the drawing, the spark plug comprises a conventional shell 10 having a large bore 12 in its upper portion and a smaller bore 14 in its lower portion. A smoothly contoured shoulder 16 is formed between bores 12 and 14. The outer surface of shell 10 surrounding the lower portion is threaded as at 18 for installation in an engine. Conventional ground electrodes 20 are formed in the lower end of smaller bore 14.

An insulator 22 made from conventional materials and having a massive body portion 24 smoothly tapering through an external shoulder 25 into a smaller tip portion 26 is mounted in shell 10 with body portion 24 positioned in larger bore 12 and tip portion 26 positioned in smaller bore 14. Shoulder 25 seats on shoulder 16 where it is sealed by a gasket 28.

An electrode passage 30 is formed longitudinally in the center of insulator 22. Passage 30' has a large diameter as at 32 at the top of insulator 22, a medium diameter 33 extending through body portion 24 and into tip portion 26, and a reduced diameter 34 in the end of tip 26. Shoulders 35 and 36 are formed in passage 30 between large diameter 32 and medium diameter 33 and between medium diameter 33 and reduced diameter 34, respectively.

A metallic cup 38, the exterior member, has an enlarged lip 39 at its open end seating on shoulder 36. The closed end of cup 38 extends out of tip 26 to terminate adjacent electrodes 20. A metallic wire 40, the interior member, is seated in cup 38 and extends upward into passage 33 above shoulder 16. Cup 38 can be made of nickel, nickel alloys, platinum, or other materials capable of resisting electrical discharge erosion and combustion gas corrosion. Nickel is preferred in the spark plug of this invention because it is easily formed and relatively inexpensive. Wire 40 can be made of copper, silver, or other materials having high electrical and thermal conductivity. In the spark plugs of this invention, copper is preferred because it has a good combination of these properties.

A heat conducting medium such as a composite 42 of metal powder and glass surrounds wire 40 to fill passage 30 between wire 40 and insulator 22. The metal powder can be copper, nickel, or other materials having good thermal conductivity. Good electrical conductivity also is desirable in spark plugs of this invention using the composite as a termination for the resistor in the manner described subsequently. The glass is an electrical grade borosilicate glass such as Corning No. 7070 glass made by the Corning Glass Company. Copper and nickel metal powders are preferred because they produce a composite having a good balance of electrical and thermal conductivity.

The composite preferably is about 30 to percent glass when copper or nickel is used as the metal powder because these compositions also provide some sealing of passage 30. This range can be adjusted somewhat depending on the desired electrical and thermal conductivity and sealing. Copper or nickel composites of about 50 to 70 percent by weight glass have an excellent balance of these properties. A copper powder having a particle size such that a maximum of 5 percent is held on a 200 mesh screen, 15-25 percent is held on a 325 mesh screen, and 70-90 percent passes the 325 mesh screen produces a useful composite when mixed with borosilicate glass to produce compositions in this range.

Mounted in passage 30 above composite 42 is an integral resistor seal 44. Resistor seal 44 can be made from mixtures of borosilicate glass, titanium oxide, and boron carbide as disclosed in Heischman, US. Patent 3,088,921, the disclosure of which is incorporated hereby into this Specification. Resistor seal 44 can contact wire 40 directly as disclosed by Heischman or composite 42 can provide a lower termination between resistor seal 44 and wire 40 as shown in the drawing. If desired, ordinary nonsealing resistors made of glass and carbon black mixtures can be used in place of the integral resistor seal but, of course, such constructions require composite 42 to seal the center wire structure.

An upper termination 46 is located in passage 30 above resistor seal 44. Upper termination 46 is a composite of metal powder and glass similar in composition to composite 42 except that a much broader range of materials and proportions can be used since it is not necessary for termination 46 to have the thermal conductivity or the sealing ability of composite 42. Mixtures of 30 percent by weight copper powder and 70 percent by weight borosilicate glass are used regularly for upper termination 46.

A stud 48 is mounted in electrically conducting contact with termination 46 at shoulder 35. The lower portion of stud 48 can be threaded, knurled, or serrated to provide the desired electrical and mechanical contact with termination 46.

A sleeve 50 is held in place at the top of shell by rolling the top edge of shell 10 over projections of sleeve 50. At its lower end, sleeve 50 contacts a gasket 52 that in turn seats on insulator 22 to position the latter in shell 10.

To assemble the spark plug of this invention, the center wire 40 is forced into cup 38 and the assembly is annealed at a temperature just below the melting point of the wire to insure intimate heat conducting contact between cup 38 and wire 40. A mixture for forming composite 42 is prepared by mixing the ingredients with a small amount of a suitable binder.

Cup 38 is dropped into passage 30 until lip 39 seats on shoulder 36. The mixture for composite 42 is placed in passage 30 on top of lip 39 and around wire 40. If composite 42 is to act as a termination for resistor seal 44, additional mixture sufficient to cover the top of wire 40 is added. A mixture forming the integral resistor seal 44 is placed on top of the mixture for composite 42, and a mixture forming upper termination 46 then is placed on top of the mixture for resistor seal 44.

The assembly then is heated in a furnace to 1600 1800 F. to melt the various mixtures in passage 30. Stud 48 is pressed into passage 30 by a ram, and the insulator assembly is cooled to room temperature while maintaining pressure on stud 48.

The entire insulator assembly then is positioned along with gasket 28 in preformed shell 10. Sleeve 50 is mounted in the top of shell 10 along with gasket 52, and the upper lip of shell 10 is rolled to attach sleeve 50 to shell 10.

Manufacturing the spark plug of this invention is simplified because an excellent heat conductivity path through wire 40 and composite 42 is provided without maintaining close tolerances on cup 38 and wire 40 for extensive distances. Composite 42 effectively compensates for variations in both the diameter and length of wire 40. Cement is not required between cup 38 and insulator 22 as the main heat path from the tip of cup 38 is through wire 40 and composite 42 to insulator 22.

Thus, this invention provides a spark plug having a short exterior member seating in the tip of the insulator with an interior member in heat conducting contact therewith extending into the massive portion of the insulator. The plug has a performance rating equivalent to plugs requiring far more complicated manufacturing techniques and much greater amounts of expensive metals.

What is claimed is:

1. A spark plug Comprising a shell,

an insulator mounted in said shell, said insulator having a massive portion and a considerably smaller tip portion, an external shoulder separating said massive portion and said tip portion and seating on said shell, and a longitudinal passage extending through said massive portion and said tip portion,

an electrode mounted in said passage, said electrode including a metallic cup seated in said passage in said tip portion and a metallic wire seated in said cup and extending above said shoulder, said wire being in intimate heat conducting contact with said cup, and

a heat conducting medium filling the space between said wire and said insulator, said wire and said heat conducting medium serving as the main heat conducting path for transferring heat from the electrode tip to the insulator massive portion.

2. The spark plug of claim 1 in which the heat conducting medium is a composite of powdered metal and glass.

3. The spark plug of claim 2 in which the powdered metal is nickel or copper.

4. The spark plug of claim 3 comprising an integral resistor seal located in said passage.

5. The spark plug of claim 4 in which the composite of powdered metal and glass forms a lower termination for the resistor seal.

6. The spark plug of claim 5 in which the percent by weight of glass in the composite is about 50 to percent.

7. The spark plug of claim 2 in which the percent by weight of metal in the composite is about 50 to 70 percent.

8. The spark plug of claim 1 comprising an integral resistor seal located in said passage.

References Cited UNITED STATES PATENTS 2,248,415 7/1941 Schwartzwalder et al.

2,321,840 6/1943 McDougal 313-145 X 2,391,456 12/1945 Hensel 313-1411 X 2,542,903 2/1951 Cipriani 313-142 X 2,864,884 12/1958 Counts et a1. 315-58 X JAMES W. LAWRENCE, Primary Examiner.

C. R. CAMPBELL, Assistant Examiner.

US. Cl. X.R.

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