US2831138A

US2831138A - Electrical connection for high energy igniters, and method for producing same

Info

Publication number: US2831138A
Application number: US485842A
Authority: US
Inventors: Richard C Teasel
Original assignee: Champion Spark Plug Co
Current assignee: Federal Mogul Ignition LLC
Priority date: 1955-02-03
Filing date: 1955-02-03
Publication date: 1958-04-15
Anticipated expiration: 1975-04-15

Description

April 15, 1958 2,831,138

EL ELECTRICAL CONNECTION FOR HIGH ENERGY IGNITERS, AND METHOD FOR'PRODUCING SAME Filed Feb. 3, 1955 FEE. I

R ICHARD C. TEASEL BY vdgum ATTORNEYS ELECTRICAL CONNECTION FOR HIGH ENERGY IGNITERS, AND METHOD FOR PRODUCING SAME Richard C. Tease], Toledo, Ohio, assignor to Champion Spark Plug Company, Toledo, Ohio, a corporation of Delaware Application February 3, 1955, Serial No. 485,842

5 Claims. (Cl. 313-130) This invention relates to an electrical connection for high energy igniters, and to a method for producing same.

A recent development in the field of spark plugs and jet engine igniters contemplates a high energy spark discharge over the surface of the nose of a spark plug or igniter. Although many advantages are achieved from using this type of discharge to fire reciprocating engines and jet engines, there are also difiiculties. When a high voltage is applied to cause the spark, serious problems are encountered in insulating the ignition system. When only a low voltage is applied the discharge must be along some semi-conducting surface, but substantial difficulties have been encountered in the production of igniters of this type. One major problem that has been encountered is the relatively rapid increase in minimum sparking voltage which occurs during use of the igniter. The term minimum sparking voltage is used herein to refer to the lowest voltage applied across the terminals of an igniter that is capable of causing a spark discharge across the semi-conductive surface. When a high energy, low voltage, igniter is in service in a reciprocating engine or in a jet engine, the useful life thereof is ended when the minimum sparking voltage exceeds the voltage available in the ignition system, usually between 1000 and 2000 volts. Therefore, the relatively rapid increase in minimum sparking voltage of high energy igniters can be, and frequently is, the limiting factor on useful life thereof.

The instant invention is based upon the discovery of an electrical connection in a high energy igniter, and of a method for producing such electrical connection, which substantially prolongs the service life thereof prior to the increase of minimum sparking voltage to any predetermined maximum. Such electrical connection is between a center electrode of an igniter and a semi-conducting sparking surface, and also between a ground electrode and such surface.

It is, therefore, an object of the invention to provide an improved electrical connection in a high energy igniter.

It is a further object of the invention to provide a method for producing improved electrical connections in high energy igniters.

Other objects and advantages will be apparent from the description which follows, reference being had to the accompanying drawings, in which- Fig. 1 is a view in section of a high energy igniter incorporating an improved electrical contact according to the invention; and

Fig. 2 is an enlarged cross-sectional view of a portion of the igniter of Fig. 1 showing a step in the production of the improved electrical connection according to the invention.

According to the invention an improved high energy igniter is provided. Such igniter comprises a ceramic insulator having a center bore, an electrically semi-conducting body constituting at least the surface of the nose portion of the insulator, a center electrode seated in the United States Patent 0 the flange 13 of the shell.

thousandths of an inch separates the electrode 19 from the lower portion of the insulating body 17 and frorit' 23 of the electrode 19 is sealed in the central hole 25 in any known manner as by a suitable sealing material'- insulator bore, and extending adjacent the conducting surface, a metal shell in which the insulator is seated, a ground electrode spaced from the center electrode and adjacent the conducting surface, a metalized coating-in terposed between the center electrode and the conducting surface, in electrical contact with each, and adhered-to at least one, and a metalized coating interposed between the ground electrode and the conducting surface, in electrical contact with each, and adhered to at least one.

Referring now to the drawings, and particularly to Fig. 1, one specific high energy igniter embodying an electrical connection according to the' invention comprises a shell 11 threaded as at 12 for engagement with the wall of the combustion chamber of a jet or reciprocating engine, and provided, in the constructionshown, with an inwardly extending lower flange 13. An insulator 15 is-seated and fixed in the shell by a compressed body of holding powder-tamped overa metal sleeve or gasket, and over which is disposed a metallic sleeve 16 threaded into the shell 11. The insulator- 15 is composed of an electrically insulating upper portion 17 and an electri-i cally semi-conducting nose portion 18, and supports a center electrode 19. In assembly, the insulator 15 is disposed so that the nose portion 18 thereof is seated against a ground electrode 20, which is in turn the nose portion 18. a The central electrode 19 may be of any suitable construction, and in the form shown is composed of aflsterh" part 23 and an integral flange 24. The stem part 23 is received in an enlarged central hole 25 of the insulator" 15, while the flange 24 bears against a flat surface of the nose portion 18 of the insulator 15. The stem part 27. A metalized coating 28, which can be of any -suit-' the insulator 15. A similar metalized coating 29 is inter-' posed between the ground electrode 20 and the nose portion 18 of the insulator 15.

- Referring to Fig. 2, the insulator 15 and-semi-conduct-f ing nose portion 18 are shownenlargedwith a metal"- coating 30 applied to the exposed portions of the-body 18. The coating 30 can be a uniform dispersion of colloidal silver in a relatively volatile hydrocarbon oil, preferably a drying oil. Such a dispersion is available commercially under the trade designation DuPont silver 4887. The dispersion can be applied to the exposed portions of the semi-conducting body 18 by dipping, brushing, spraying, or in any desired manner. The viscosity of the dispersion, and with it the thickness of the coating 30, can be varied by suitable regulation of the ratio of silver, oil and solvent, for example turpentine, in the case of most drying oils. Similar dispersions of platinum, gold and copper have also been used, but most satisfactory results have been achieved with the silver dispersion.

After the insulator-semi-conducting body assembly (which can be produced, for example, as described in a co-pending application entitled Electrically Semi-Conducting Body, Serial No. 386,189, filed October 15, 1953, by Harry G. Schurecht) has been coated as described in the preceding paragraph, the electrode 19, which can be silvered in the same manner, if desired, is inserted in a central bore of the insulator, and the holding powder 27 tamped in place. The resulting assembly is then heated to volatilize the oil in the silver or other dispersion, for example to a temperature from about 1200 Patented Apr. 15,1958

forced against An air gap 21 of a few 3 F. to about'1400 F. for approximately fifteen minutes.

The electrode-insulator assembly is then locked in the shell 11 as shown in Fig. 1.

After the igniter has been assembled as described the silver or other metal coating is removed, for example, by mechanical abrasion, from the exposed portions of the insulator, leaving the coating intermediate the ground electrode and the conducting body 18, and also intermediate the center electrode 19 and the semi-conducting body 18.

It has been found as the result of extensive engine tests that igniters having a metalized coating positioned according to the invention have substantially increased useful life over identical igniter-s produced without such coating, the increase being of the order of 50 to 75 percent when the metalizing is with silver, as specifically described.

It will be apparent that various changes and modifications can be made from the specific details shown in the attached drawings and discussed in the specification without departing from the spirit of the invention. For example, various metals can be used in place of silver, gold, platinum and copper, previously mentioned specifically, so long as such metal does not oxidize or melt at temperatures encountered in service of an igniter, usually in the vicinity of 1500 F. to 1600 F. Preferably, the metalized coating comprises a metal from group 1(b) of the periodic system having an atomic number from 29 through 79, inclusive, i. e., comprises copper, silver or gold, and most desirably silver or gold. The hydrocarbon drying oil disclosed specifically acts only as a temporary binder to hold the finely divided silver particles in place prior to firing. Other temporary binders, for ex ample a dextrine solution in water, could be used for this purpose.

While the invention has been described inconnection with a body of substantial size of electrically semi-conducting material along the surface of which a spark discharge occurs, it is equally operable when a semi-conducting engobe coating having a thickness of, at the most, a few thousandths of an inch is used in place thereof. In such case it is usually preferred to leave at least a small gap between the portion of the coating that will ultimately contact the center electrode and the portion that will contact the ground electrode. The high energy spark that occurs across the engobe surface will then vaporize in a short time any metalized coating that is exposed. If desired, a solvent can be used to remove the exposed portion of the metalized coating, for example after assembly of the igniter. The final metalized coating in the igniter is present only on portions of the body which are in contact with the electrodes, the surface of the semi-conducting body along which a spark discharge occurs not being metalized.

What I claim is:

l. A high energy igniter comprising a ceramic insulator having a center bore, an electrically semi-conducting body constituting at least the surface of the nose portion of said insulator, a center electrode seated in said insulator bore, and extending adjacent said conducting surface, a metal shell in which said insulator is seated, a ground electrode spaced from said center electrode and adjacent said conducting surface, a metalized coating interposed between said center electrode and said conducting surface, in electrical contact with each, and adhered to at least one, and a metalized coating interposed between said ground electrode and said conducting surface, in electrical contact with each, and adhered to at least one.

2. A high energy igniter as claimed in claim 1 in which each of said metalized coatings is adhered to said conducting surface.

3. In a high energy igniter including a ceramic insulator having a center bore, an electrically semi-conducting body constituting at least the surface of the nose portion of the insulator, a center electrode seated in the insulator bore, and extending adjacent the conducting surface, a

metal shell in which the insulator is seated, and a ground electrode spaced from the center electrode and adjacent the conducting surface, the improvement comprising a metalized coating interposed between the center electrode and the conducting surface, in electrical contact with each, and adhered to at least one, and a metalized coating intei= posed between the ground electrode and the conducting surface, in electrical contact with each, and adhered to at least one.

4. In a high energy igniter, the improvement as claimed in claim 3 in which each of said metalized coatings is adhered to the conducting surface.

5. In a high energy igniter, the improvement as claimed in claim 4 in which the metalized surface is composed of a metal from group 1 (b) of the periodic system having an atomic number from 29 through 79, inclusive.

References Cited in the file of this patent UNITED STATES PATENTS 2,356,053 Hastings et al. Aug. 15, 1944 2,578,754 Smits Dec. 18, 1951 2,684,665 Tognola July 27, 1954 2,733,369 Smits Jan. 31, 1956 FOREIGN PATENTS 724,211 Great Britain Feb. 16, 1955