US3124718A - Combination spark - Google Patents

Description

March 10, 1964 B. H. MARKS ETAL COMBINATION SPARK PLUG AND ELECTRICAL ELEMENT Original Filed Jan- 12,' 1960 2 Sheets-Sheet 1 I ll Fm Z luvemoes 6am HMARKS LEONARD J. SPERRY BY 7% 42412-942 ATTORNEY United States Patent 3,124,718 COMBENATHON SPARK PLUG AND ELECTRECAL ELEMENT Bert H. Marks and Leonard J. Sperry, Milwaukee, Wis,

assignors to Globe-Union, Inc., Milwaukee, Wis, a corporation of Delaware Original application Jan. 12, 196i), er. No. 1,903, now Patent No. 3,013,131, dated Apr. 27, 1969. Divided and this application Mar. 30, 1961, Ser. No. 112,141

3 Claims. (1. SIS-3) This invention relates to spark plugs which incorporate within their bodies electric circuit elements, and particularly to such plugs which are essentially no larger than a conventional spark plug and the electric circuit element incorporated therein limits the current passing through the center electrode to adapt the plugs for use in a distributorless ignition system. This application is a division of Marks et al. application Serial Number 1,903, filed January 12, 1960.

In a distributorless ignition system where a single power supply is continuously connected to a multiplicity of spark plugs it is necessary to provide current limiting condensers or resistors or inductors in series with each plug to cause all the plugs to spark simultaneously as stated in Uni ed States Patents No. 2,866,839 and No. 2,866,447. These current limiting electric circuit elements have been connected in the electrical circuit unshielded and physically separated from the spark plugs and have consequently been subjected to severe moisture, temperature and vibration conditions. There has also resulted increased radio interference, excessive power loss, spark-over, susceptibility to breakage, and impractical usage of space.

One object of this invention is to eliminate or minimize the harmful ef ects of moisture, temperature and vibration encountered by existing systems in which separate electrical circuit elements are used in circuit with the spark plugs and to reduce the bulk of such systems.

A further object is to insulatively mount an electrical circuit element within a spark plug in a manner which prevents spark-over, excessive power loss, and susceptibility to breakage.

These objects are accomplished by mounting the electrical circiut element in a space within the ceramic insulator of a spark plug or by using such insulator as an integral part of such element. Thus the insulator provides protection and physical support for the element, and space requirements are minimized. The element may be cushioned within the insulator by an insulating and shock absorbing material to protect it from moisture, vibration and bad effects of temperature. In case the element is a capacitor, voltage breakdown can be lessened by utilizing part of the insulator as the dielectric. However, by mounting a unitized capacitor entirely within the spark plug insulator the insulating material will provide adequate voltage breakdown and spark-over protection from electrode to electrode of the capacitor.

Other objects and advantages will be pointed out in or be apparent from the specification and claims, as will obvious modifications of the four embodiments shown in the drawings of which:

FIG. 1 is a partial sectional view of a spark plug embodying the present invention;

FIG. 2 is a sectional view showing another embodiment of the present invention;

FIG. 3 is a sectional view showing a third embodiment of this invention in which a portion of the insulator is not shown;

FIG. 4 is a sectional view of a fourth embodiment of the present invention.

The thicknesses of all metalized coatings, silvered sur- 3,124,718 Patented Mar. 10, 1964 faces, and bonding pastes are exaggerated in the drawings for the sake of clarity.

Referring to the drawings, FIG. 1 shows the preferred embodiment of this invention in which the center electrode assembly comprises an insulator 1d and center electrode 18. The insulator 19 has a bore 12, a first counterbore 14 and a second counterbore 16. The center electrode 18 is mounted in bore 12 and has a head 2% which extends into the first counterbore 14 to retain electrode 18 in place. Powdered conductive glass is placed in first counterbore 14 and an electrically conductive shank 22 having head 24 is pre-pressed into the glass powder. insulator it) is then heated toaround 1500" Fahrenheit and the shank is pressed inwardly to firmly seat shank head 24 on a tapered shoulder 25 in the insulator. This provides a hermetic seal between the center electrode and the insulator.

A metal shell 26 is then applied to the insulator in a conventional manner and a ground electrode 27 is properly gapped from the center electrode 18.

After the metal shell is applied to the insulator capacitor unit indicated generally at 28 is mounted in counterbore 16. This unit includes a high-K ceramic slug 30 having silvered ends or electrodes 32 and 34. This capacitor is relatively small; about 0.250 inch in diameter and 0.400 inch in length. It may have a rating of from 10 to 50 mmf. A thin copper ribbon 36 is soldered to end 32., and a fiat headed screw 38 is soldered to end 34. Screw 38 is screwed into the head of shank 22 which is drilled, countersunk and tapped to receive it. The ribbon projects beyond the end of the insulator 1d. The space in counterbore 16 around the capacitor unit is filled with a igh voltage insulating material to prevent spark-over along the sides of ceramic slug 3i? and along the counterbore wall. A material found highly desirable for this purpose is a mixture of silicone oil and uncured silicone rubber. This mixture is a fairly thin liquid which is poured into counterbore 16. The spark plug is then heated to cure the silicone material into a resilient rubber capable of withstanding the high temperatures and voltages encountered in the spark plug stem. Better bonding of the silicone rubber to the bore and ceramic slug walls is secured if a suitable primer wetting agent is used to coat these walls before pouring the silicone mixture into counterbore 16.

After the rubber is cured, a terminal unit is bonded to the insulator stem by adhesive 31. This unit comprises a cap 29 having a central opening and a threaded terminal 33 having a bore 39. This terminal is secured to the cap with the opening and central bore aligned so that when the unit is placed over the end of the insulator the conductive ribbon 363 is threaded through the terminal. Ribbon 36 is then soldered at 53 to terminal 33 and cut off.

Connection of capacitor unit 28 to terminal 33 as described permits the relative motion between the component parts of the spark plug, caused by the different coefficients of expansion of the various components, to occur without damaging the connection between terminal 33 and capacitor unit 28. The stresses ordinarily caused by vibration and relative motion of the parts are relieved by the resilient insulating material. The capacitor being mounted within the insulator and hermetically sealed will not be affected by moisture.

Spark-over along the outside of insulator 10 is pre vented by providing an indentation in the insulator in which silicone rubber washers 37 are mounted.

The center electrode assembly shown in FIG. 2 is constructed similarly to that shown in FIG. 1. The insulator 47 has a bore 41, a first counterbore 43 and a second counterbore 45. A center electrode 19 is mounted in the bore 41 in the same manner electrode 13 is mounted in the bore 12. Powdered conductive glass 15 is placed in first counterbore 43 and a headed stud 48 is pressed into the glass powder. These components are then heated as previously described to seat the head of the stud 43 on the shoulder between the first and second counterbores. A ceramic slug 42 with silvercd ends or electrodes and 56, substantially identical with ceramic slug 3%, has its end 46 secured to headed stud by conductive paste 5% or by soldering and its other end 44 is secured directly to a threaded terminal 52 by conductive paste 5% or the like. Finely ground mica is compacted around slug 42 and the head of terminal 52 and dried. A fluorchemical is then applied to saturate the mica thereby providing a good high voltage insulating material indicated as 54. The center electrode assembly is next placed in a vacuum and an epoxy seal 56 is made between the terminal 52 and the insulator d7 thereby preventing the ingress of air inside the insulator and also supporting the terminal. Epoxy resin and silicone material are also good high voltage insulators and may be substituted for the mica and fluorchemical mixture 54.

A capacitor may also be built into the center electrode assembly by using the insulator itself as the dielectric of the capacitor. In FIG. 3 the insulator 6% has a bore 61, a first counterbore 63 and a second counterbore 65. An internal electrode 62 is bonded to the inner side of the wall of the second counterbore and an external electrode 58 is bonded to the outside of such wall opposite the inner electrode. A center electrode 67 is secured in bore 61 and a headed stud 64 is sealed in conductive glass 66 in the manner heretofore described; the head of stud 64 being in good electrical contact with the electrode 62. A cap 68 with a threaded terminal 70 secured thereto fits over the end of the insulator and is soldered to the electrode 58 to form a seal and a conductive contact therewith. A protective insulating glaze 72 covers electrode 58 thereby protecting it from deleterious forces and preventing fiashover to the metal shell in which the assembly is mounted. In order to provide suflicient capacity, the spark plug insulator 60 must be longer than that used in conventional spark plugs. The increased length is also necessary to provide enough space between cap 68 and electrode 62 to prevent spark-over. This spacing may be minimized by using insulating material 76 between the cap and electrode 62.

In FIG. 4 a center electrode assembly is shown in which the dielectric of the capacitor also is formed by the insulator. In this modification a two-piece insulator is used which provides an end wall as an additional dielectric thereby cutting down on the required length of the insulator and lessening the chances of spark-over. The insulator consists of a top piece 86 open at only the lower end and a bottom piece 99. The inside of piece 86 including its end wall 38 has a metalized coating or electrode 78. The outside of piece 86 including its end wall has a metalized coating or electrode 82. An insulative coating $8 is applied over electrode 82 to prevent spark-over along the outside of the insulator stem. The bottom piece 90 of the insulator has a boss 94 which projects into the open lower end of top piece This piece has a bore i l in which a headed center electrode 92 is sealed with its head projecting from the boss 94 and engaging the electrode 73 when the pieces are assembled as shown.

This construction permits reduction of the length of the insulator to approximately that of a conventional spark plug due to the increased capacity secured from top end A cap 84 with a terminal fits over the end of the insulator and is soldered to the electrode 82. However t.1e end wall 8% completely insulates cap 24 from electrode 73 thereby eliminating the spark-over problem.

Although but four embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of appended claims.

We claim:

1. In a spark plug of substantially conventional size and shape, a unitary center electrode assembly comprising, an insulator having a bore, a center electrode mounted in said bore and projecting from one end of said insulator, a terminal on the other end of said insulator, a capacitive electrical current limiting element incorporated within said insulator and connected in series between said center electrode and said terminal, said current limiting element including a metallized coating on a portion of the outer surface of the insulator and a metalized coating on a portion of the inner surface of said insulator, said outer surface metalized coating being connected to said terminal, and said inner surface metalized coating being connected to said center electrode, whereby a portion of the insulator itself forms the capacitor dielectric.

2. The center electrode assembly according to claim 1 in which said insulator is a unitary structure having a central bore with a first counter bore for supporting the center electrode and a second counter bore for supporting the metalized coatings.

3. The center electrode assembly according to claim 1 in which said insulator is in two pieces, one piece carrying said metalized coatings and having a closed end, the other piece being adapted for connection to said one piece, said other piece carrying said center electrode and holding it in contact with said insulator bore metalized coating.

References Cited in the file of this patent UNITED STATES PATENTS 1,317,834 Sweeney Oct. 7, 1919 1,783,525 Stewart Dec. 2, 1930 FOREIGN PATENTS 277,442 Great Britain Sept. 2, 1927

Claims (1)

1. IN A SPARK PLUG OF SUBSTANTIALLY CONVENTIONAL SIZE AND SHAPE, A UNITARY CENTER ELECTRODE ASSEMBLY COMPRISING, AN INSULATOR HAVING A BORE, A CENTER ELECTRODE MOUNTED IN SAID BORE AND PROJECTING FROM ONE END OF SAID INSULATOR, A TERMINAL ON THE OTHER END OF SAID INSULATOR, A CAPACITIVE ELECTRICAL CURRENT LIMITING ELEMENT INCORPORATED WITHIN SAID INSULATOR AND CONNECTED IN SERIES BETWEEN SAID CENTER ELECTRODE AND SAID TERMINAL, SAID CURRENT LIMITING ELEMENT INCLUDING A METALLIZED COATING ON A PORTION OF THE OUTER SURFACE OF THE INSULATOR AND A METALIZED COATING ON A PORTION OF THE INNER SURFACE OF SAID INSULATOR, SAID OUTER SURFACE METALIZED COATING BEING CONNECTED TO SAID TERMINAL, AND SAID INNER SURFACE METALIZED COATING BEING CONNECTED TO SAID CENTER ELECTRODE, WHEREBY A PORTION OF THE INSULATOR ITSELF FORMS THE CAPACITOR DIELECTRIC.

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