US3173056A

US3173056A - Spark plug containing electrical resistor

Info

Publication number: US3173056A
Application number: US48913A
Authority: US
Inventors: Henry M Dressel
Original assignee: Stackpole Carbon Co
Current assignee: Stackpole Carbon Co
Priority date: 1960-08-11
Filing date: 1960-08-11
Publication date: 1965-03-09
Anticipated expiration: 1982-03-09

Description

March 9, 1965 H. M. DRESSEL SPARK PLUG CONTAINING ELECTRICAL RESISTOR Filed Aug. 11, 1960 INVENTOR. f/'A/RV M. OQESSEL United States Patent 7 3,173,056 SPARK PLUG CONTAINING ELECTRICAL RESISTOR Henry M. Dressel, St. Marys, Pa., assignor to Staclrpole Carbon Company, a corporation of Pennsylvania Filed Aug. 11, 1960, Ser. No. 48,913 4 Claims. ((31. 315-58) This invention relates to spark plugs, and more particularly to those containing electrical resistors to prevent electrical interference with television reception.

Ordinary automotive spark plugs are instrumental in generating in the ignition system high frequency electric currents that are in the television broadcast bands and which therefore will interfere with both the picture and the sound in television receiving sets when the vehicle containing the plugs is in the neighborhood of the sets. To prevent such interference, it is the general practice to insert an electrical resistor in the porcelain core of a spark plug. Such a resistor is effective for its intended purpose, but usually not for the length of time that the spark plug is used. The ends of the resistor are sprayed with a material of low electrical resistance, generally Monel or nickel, to form low resistance end contacts that electrically connect the resistor to the center electrode and the upper terminal of the plug. As the plug is used in service, the air in the chamber containing the resistor is ionized and in time will cause the contacts to corrode and even disappear. In some cases the ends of the resistance material itself become deteriorated too. The result is that the electrical resistance of the resistor ultimately increases to a very great extent. This not only keeps the resistor from performing its intended function, but it also interferes with proper operation of the spark plug.

It is among the objects of this invention to provide a resistor spark plug in which the useful life of the resistor is prolonged greatly.

In accordance with this invention an electrical resistor, having low resistance end contacts, is disposed in a chamber in the tubular porcelain core of a spark plug. The resistor contacts are electrically connected with the inner ends of an electrode and a terminal, which are sealed in opposite ends of the core. Dielectric material is placed in the chamber to exclude all air from the resistor contacts so that they will not be alfected adversely. Preferably, all air space in the chamber is filled with a dielectric grease or the like that has high viscosity at both high and low temperatures.

The preferred embodiment of the invention is illustrated in the accompanying drawing, in which the single figure is a side view of a spark plug, with the upper portion of the core shown in central longitudinal section.

Referring to the drawing, a conventional spark plug has a tubular porcelain core 1, the lower portion of which is sealed in a tubular metal base 2 having a threaded lower end to permit it to be screwed into the upper end of a cylinder in an internal combustion engine, such as an automobile engine. A rod-like center electrode 3 extends lengthwise of the core and is sealed in its lower portion. The lower end of the electrode projects a short distance below the metal base and is spaced from a second electrode 4 connected to the base to form the usual spark gap. The upper end of the center electrode projects slightly into the lower end of an axial chamber 6 in the core. The customary electric terminal '7 is screwed into the upper end of the core and sealed therein. Inside the chamber there is a cylindrical resistor having a carbonaceous body 8, on the opposite ends of which there are extremely thin contacts 9 that may be formed by applying low resistance material to them, such as by 3,173,056, Patented Mar. 9, 1965 spraying Monel, nickel .or the like thereon. The upper contact is pressed against the lower end of terminal 7 by a coil spring 10 compressed between the lower end of the resistor and the upper end of the center electrode 3. The resistor spark plug described thus far is conventional.

It is a feature of this invention that oxidation or disappearance of the resistor contacts 9 is greatly retarded or eliminated by excluding air from them. This is done most conveniently by filling all of the air space in chamber 6 around the resistor and the spring with a material 12. having high dielectric strength. The material is poured or injected into the chamber in a liquid or plastic condition and should be viscous enough to avoid leaking from the plug. The properties of the material should be such that its viscosity will not be reduced appreciably at the high temperatures at which the plug operates. Various materials may be used for this purpose, one being grease such as Essos Nebula or Shells Darina. Those greases have high dielectric strength and maintain their viscosity at high temperatures. Oil can be used if one can be certain that no leakage will occur. Dielectric synthetic plastics, such as Dow Cornings DC4, are satisfactory.

Dow Corning also sells a dielectric gel that can be used in a spark plug. It is called Sylgard 51 and comes in liquid state. After being mixed with a catalyst it is poured into the plug chamber, which is then heated to convert the mixture into a gel.

Another unexpected result of this invention is that the substitution of material of high dielectric strength for the air in the core chamber 6 materially increases the electrical capacitance of the spark plug between the grounded metal base 2 and the electrical conductors inside the porcelain core, which helps to suppress the interference caused by the radiations from the ignition cable connected to the plu It has been found that when the resistor contacts 9 are protected from the deleterious efiects of ionization by eliminating air space around them, the resistor will last as long as the spark plug is likely to be used. There is very little change in the resistance of the resistor in 10,000 miles of driving of a car containing such a plug.

According to the provisions of the patent statutes, I have explained the principle of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. In a spark plug, the combination with a tubular porcelain core, an electrode sealed in one end of the core and projecting therefrom, an electric terminal sealed in the opposite end of the core and projecting therefrom, the core having an axial chamber between the inner ends of the electrode and terminal, a carbonaceous electrical resistor disposed in said chamber and having low resistance end contacts, and a coil spring compressed between the inner end of the electrode and the adjacent end contact of said resistor to electrically connect them and to press the opposite end contact of the resistor against the inner end of said terminal, of viscous dielectric material filling said chamber around the resistor and excluding all air from said contacts to prolong the useful life of the resistor.

2. In a spark plug according to claim 1, said dielectric material being grease.

3. In a spark plug according to claim 1, said dielectric material being a dielectric gel.

3,1 3 4. In a spark plug according to claim 1, said dielectric material having high viscosity at both high and low temperatures.

References Cited by the Examiner UNITED STATES PATENTS 1,927,297 9/33 Rabezzana 31558.1 X 2,442,015 5/48 Peters et a1. 315-85 4 Brinson. Cipriani et a1 31558.1 Peterson 17484 Marks et a1. 315-58 Brown 17475 X DAVID J. GALVIN, Primary Examiner. ARTHUR GAUSS, Examiner.

Claims

1. IN A SPARK PLUG, THE COMBINATION WITH A TUBULAR PROCELAIN CORE, AN ELECTRODE SEALED IN ONE END OF THE CORE AND PROJECTING THEREFROM, AN ELECTRIC TERMINAL SEALED IN THE OPPOSITE END OF THE CORE AND PROJECTING THEREFROM, THE CORE HAVING AN AXIAL CHAMBER BETWEEN THE INNER ENDS OF THE ELECTRODE AND TERMINAL, A CARBONACEOUS ELECTRICAL RESISTOR DISPOSED IN SAID CHAMBER AND HAVING LOW RESISTANCE END CONTACTS, AND A COIL SPRING COMPRESSED BETWEEN THE INNER END OF THE ELECTRODE AND THE ADJACENT END CONTACT OF SAID RESISTOR TO ELECTRICALLY CONNECT THEM AND TO PRESS THE OPPOSITE END CONTACT OF THE RESISTOR AGAINST THE INNER END OF SAID TERMINAL, A VISCOUS DIELECTRIC MATERIAL FILLING SAID CHAMBER AROUND THE RESISTOR AND EXCLUDING ALL AIR FROM SAID CONTACTS TO PROLONG THE USEFUL LIFE OF THE RESISTOR.