US2380579A - Spark plug - Google Patents

Description

July 31, 1945. fiV

c. clPRlANl 4 2,380,579

SPARK L-UG Fiied June le, `1942 tv fr INVENTOR "ESTER CIPRIANI AT ORNEYS Patented July 31, 1945 AUNITED STATES PATENT 1 OFFICE SPARK PLUG 4chester Cipriani, Toledo, ohio Application June 16, 1942, Serial No. 447,211

(Cl. 12s- 169) 14 Claims.

of sealingmethods developed in the art. In some methods, the sealing portion is conductive and becomes a part of the center electrode, while in others a metal center electrode extends completelyv through an aperture in the insulator core. In the first method a seal'to be successful must have relativelyv low resistance and constituted so that the expansion characteristic under temperature change substantially matches that o f the insulator whereby the sealing material remains under substantially constant pressure. In the second method, the metal ol the center wire usually has a much greater coefficient of expansion than the insulatorin which it is positioned so that a variable space between the two members results, which must be closed to provide a seal. The sealing material must have such characteristics to compensate for the changes in volume of the varying space at the different temperatures Within the operating range.

Glass containing a conductor either as graphite or powdered metal has been used for the purpose of sealing according to the rst method. Powdered metal alone has also been used for this purpose. a metal beingselected which has a temperature coellicient of the proper value to match the coefficient of the insulator. However powdered metal alone is not entirely successful' because only metals which are very expensive appear to have the right properties to match the properties of the insulator body. Glass with interspersed metal requires a high temperature to fuse the seal in position.

The presnnt invention provides a4 novel method ol sealing spark plug electrodes in position which allows accurate control of the coefficient of expansion of the sealing material so that practically lperfect matching may be. obtained. The sealing which will give a coefcient of expansion falling between the separate coeicients of expansion of the two materials forming the sealing mixture. Knowing thecoeicient of spatial expansion of the insulator, a. mixture can be selected which will match this with reasonable accuracy so that a substantially perfect seal will result, even though the temperature may vary within wide limits.

Another aspect of the invention relates to the use of a cement, such as a sodium silicatecement. or a sodium silicate cement containing sodium silica-fluoride in combination with a metal powder or a conducting powder dispersed through the body of the cement. This cement is then used alone or in combination with a powdered conducting mixture as described above to form the seal. It has been discovered that if the powdered mixture is compacted into position above the cement while the cement is still wet that a better seal is obtained which under tests shows itself to be substantially immune to gas leakage to form a substantially perfect seal. When combined with the conducting powder mixture compacted in position either Vcement alone or cei" ment with interspersed conducting material may be used. It is however preferable to use cement* alone when combined with the compacted vconducting powder. l

1t is therefore a principal object of this invention to providea methodoi sealing center elec-` trodes in spark plug insulators by the use ofr a i powdered mixture of two or more materials having dissimilar coeilicients of expansion.

It is a further object of this invention to provide a method of sealing center electrodes in spark plug insulators which comprises compact-- ing a mixture of two powdered materials having relatively widely separated coeflicients of expansion into sealing relation, so that the sealing mixture compacted in position may have a coeflicient of expanison varying from the extremes by controlling the percentages of materials mixed together.

It is a further object of this invention to provide a method of sealing center electrodes in spark plug insulators which comprises a mixture of two powdered materials having relatively widely separated coeicients of expansion, one of vwhich is preferably of metal, so thata compacted sealing `mixture can be providedto substantially match the coefiicient of expansion4 'of theinsuy for conducting electric currents through the insulator. It is therefore a further` object of this invention to provide a method ofsealing center electrodes in spark plug insulators which uses an air-setting or chemically-setting cement having interspersed through its body a conducting material, preferably either a non-metallic powder such as graphite, or a powdered metal such as copper.

It is a further object of this invention to provide a method of sealing a center electrode into an insulating bodyv of a spark plug which comprises using cement around the body of the electrode between the electrode and the insulating body, and then positioning thereabove a compacted body of powdered material while the cement is still wet, the powdered material consisting oi a mixture of two or more comminuted substances having relatively widely separated coeilicients of expansion, 'and substantially matching the coeillcient of expansion oi the mixture by using various proportions `to that of the insulating body in which it is to be compacted.

Other objects and advantages of this invention relating to the arrangement, operation and function of the related elements of the structure. to various details oi' construction, to combinations of parts and to economies of manufacture, will ire-apparent to those skilled in the art upon consideration of the following description and appended claims, reference lbeing hadvto the accompanying drawing forming a part of this specication wherein like reference characters designate corresponding parts in the several views. l

Fig. 1 is a cross-sectional elevation of an aviation type plug to which the invention `has been applied;

Fig. 2 is an exploded view oi' the central portion of Fig. 1;

Fig. 3 is a cross-sectional elevation of a modi tlcation of the invention as applied to an automotive spark plug: and

Fig. 4 is a cross-sectional elevation of another modiilcation of the invention.

Referring to the drawing, particularly to Fig.l l, an aviation type plug is shown which comprises generally an externally-threaded tubular basey l member I0 and an upwardly-extending sleeve like gland member Il, which is in threaded cooperation with the base member III adjacent the upper portion of the base member I0. The base' member I0 is provided with an internally extending annular shoulder I2, within its externallythreaded portion Illa upon which rests an insulating member I3, which is provided with an outwardly extending protuberance resulting' in shoulders Il and Ila. The shoulder I4 cooperates with the shoulder I2 on the base member.

and'preferably a gasket member I5 is positioned 60 s..

between the shoulders to form a leak-proof seal between the base member I0 and the insulator I3.

I'he shoulder Ila corresponding to lower shoulder Il is positioned a short distance above a second inwardly extending shoulder I6 formedon the into the bore of the base member I0 to piace pressure upon the upper shoulder I4a`of the insulator. Theannular rigid member IB provides one element of this 'resilient means, the other two elements being a second annular member I9 which cooperates with the lowerend of the gland member II, and an' intermediate spring member 20 in the nature oi' a Bellville washer. y'The upper surface of the rigid annular member I8 is provided with an inclined surface IBa (Fig. 2) .hav-

ing its highest pointl adjacent to its inner edge. y

The upper rigid member I9 is similarly provided with an inclined surface ISa on its lower side, the lowest point of this oblique surface being located adiacent to the outer peripheral' edge oi the member. A

In 'considering this` resilient means consisting of the three members, I8, I9, and 20. when they are placed in cooperative relation on the upper shoulder I 4a of insulator I3, it will bef-clear that any downwardly-acting force created by gland member II will act upon the upper surface of the member I9 and will fbe transmitted to the outer-edge of the Bellville washer 20, inasmuch as the lowest point of the member 'I9 is located adjacent the periphery. The downwardly-acting force will be transmitted from the-Bellville washer 20 to the lower member Iladjacent to the inner edge of the member I8 so that a .couple is provided which tends to twist Bellville washer 20 through the action of these two forces. 'I'he Bellville washer 20 being made of resilient steel, such as tool steel lor Inconel, will form aresilient cushion for the pland member II which thrusts downwardly on the upper shoulder otvllay ofthe insulator Il so as to hold the lower shoulder Il ofthe insulator against the shoulder I2' of the base member I0 with a predetermined force. In

this way the insulator may be thrust against the` der I2., even though there is a failure of the Bellville washer. l

The tubular gland member II.' which threads into the upper portion of the base member III is provided with an internal-ceramic sleeve 2| held in concentric relationwith the inside bore of the base member I 0. Gasket member I1 is provided for the shoulder Ila of the insulator, which cooperates with a rigid annular member IB, preferably made of hardened steel or the like. To urge the insulator I3 against the shoulder I2 on the base vmember I0, a resilient means is provided between the upper shoulder Ila of the inmlator and the threaded gland member I I. which by means o! its threaded relation with the base member Il is capable ot being advanced inwardly gland member by spring members 22 which ilt between thesleeve and the gland. membebz Adlecent the upper end of the gland member an internal ilange 23 is provided integral therewith. against which the upper end of the ceramic sleeve 2I rests to prevent longitudinal movement. The lower end oi' the ceramic sleeve 21| rests on the upper side of the annular rigid member I9. lhorizontal tangs 2l integral with the spring members' 22 being positioned between the two Darts as shown.l Similarly on the upper end of the horizontal tangs 24 are positioned between the upper end of the sleeve and the internal ilangell. 'l'he length ofthe sleeve 2l is slightly less than the distance between the il'ange 23 and the bottom end of the gland member II, so that as the=gland member is screwed into the base member I0, theforce urging rigid member I8 downwardly against the Bellville washer 20 will not be carried by the ceramic sleeve. The sleeve may be glazed ii' desired on tithei its inner or outer` sides or both.

The tubular gland member I I, is preferably provided with a series of vertical serrations 25 to lit a special wrench whereby torque may be applied to the member to screw it into the base member during assembly of the plug.

The invention relating to the methods and means for sealing the insulator in the shell is described and claimed in a copending application Serial No. 482.688, filed April 12, 1943, being assigned to the same assignee.

The insulator I3 is provided witha central bore 26 having an internal shoulder 2l adjacent but preferably slightly above the external shoulder i4 to give greater strength to the insulating body.

' Anv electrode member 28 is provided to iit into the bore, having a shoulder 29 to cooperate with the internal shoulder 21 of' the insulator to hold the electrode in position. The lower end of the electrode member 28, extends beyond the tapering lower end of the insulator and may be provided with a corrosion resistant tip 30a such as tungsten or the like which may be conveniently welded in position.

Thev tip 30 cooperates with a xed, electrode which may be in the form of a ring having Aseveral inwardly projecting prongs 32 having surfaces parallel to the outer surface of the tip 36a to form spark gaps over which the ring occurs during the use of the plug in an engine. The fixed electrode is preferably brazed or hard soldered in position on a shoulder 33 in the lower inner end of the shell I asis Well known in the art. Usually a corrosion resistant material is used for this electrode to give long life.

The electrode member 28 is preferably made of material having a coefficient of expansion substantially matching that of the insulator, and is loosely tted into the bore 26 of the insulator.

Before being dropped into position the electrodev short distance 35 as shown, this is preferably acf complished by washing the cement out of the insulator bore by means of dipping into water.

Although the cement positioned between the central electrode 28 and the bore 26 gives a partial seal, there is not suiiicient cement present to give a seal having permanent holding and sealing qualities. A further agency is provided for the purpose of making a seal which will be certain and which will have durability. The cement body however does provide a heat conductor between the center electrode and the insulator body which value'suitable for use in spark plugs land hav-- the coeflicient of expansion of talc.

allows escape of heat being conducted from the inner end of the center electrode to the body of the plug and so prevent damage to the upper portion of the plug.

To assure absolute certainty in the sealingT of the bore of the insulator a second sealing body 36 is positioned in the bore above the upper end of the electrode 28, the sealing body being given conducting properties so that it may become a portion of the central electrode positioned in the bore 26 `of the insulator to carry electric currents to the-inner sparking end of the plug. Inasmuch as it is preferable to match with reasonable accuracy the coeflicient of expansion of the sealing body 36 with that of the insulator body a novel material was discoveredwhich could be controlled in this respect. To attain this end two materials,

constituent materials must necessarily be a good,

conductor of electricity, and the resistance of the resulting mixtures must be such as tobe within reasonable limits.

Three substances have been found particularly suitable for this purpose, talc being the common constituent, combined with either graphite or powdered copper to give a body withy a resistal ing a coefficient of expansion substantially matching that of the insulator to be used in the plug.

A mixture of talc and graphite may have a coefficient of expansion varying from 3. 10-6 the coeicient of expansion oi graphite to 4 106,

The resistance value of the mixturemust be taken into consideration in selecting the percentages of graphite and talc to be mixed together. The resistance of a mixture of graphite and talc has relatively unil and 5% graphite by weight could therefore be used with good results in insulators having a coeflicient of expansion of 4. 106 such. as for example mullite or Zircon insulators.

A mixture of `talc and graphite would not be suitable for insulators of alumina or magnesia which have coeincient of expansion of '75x10-s and 8.5 1()6 respectively. However a mixture of talc and powdered copper. has been found successful where the `coefficient of expansion of a mixture can be varied from 16.6 x 106 which is the coeioient of expansion of powdered copper to l. 10'6 the coeflicient of expansion of talc. The resistance value of the mixture must again be taken into consideration, the resistance values having a slowly rising characteristic and becomeis one suitable for use witheither an alumina or magnesia insulator.

The sealing body 36 may comprisethe above mentioned mixture, and is then compacted in position in the bore 26 in any convenient manner either while the cement body 34 is wet or dry.

It has been discovered that if the sealing body is compacted into the bore 26 while the cement body is still Wet, a better seal is obtained which is substantially free of gas leakage. The reason for this is not known but this procedure results in substantially leak-proof seals for the center electrode, and is therefore preferred.

To make electrical contact with the sealing body 36 a small ydisc of metal foil 31 is rmly pressed upon its upper surface, and a-coi1 spring 38 or its equivalent is positioned above in slightly contracted condition being held by a contact button 39. The Contact button 39 may either be threaded into the bore 26 and cemented in position or fused therein by means of a '(1100" Fahr.) glass frit 39a having a low melting point.` The upper surface 40 is adapted to make contact with a cable insert (not shown) which enters the gland member Il and being attached thereto by placed by a cement body 42 interspersed with a conducting substance such as graphite or pow-` dered copper. The cement is either a sodium silicate which sets by evaporation of water or sodium silicate containing sodium silica-fluoride,

.which sets by a chemical reaction. To these cements are added lapproximately by weight of either graphite or copper. The electrode is covered with this mixture and dropped into position in the central bore 43 of an insulator 42 of a conventional typeautomobile spark plug. A binding post 44 is then screwed in position while the cement is still wet. A point-45 may be provided on its lower end so that the post may be screwed into position and a good electrical contact assured. The cement adjacentzthe lower tip of the insulator 46 may again be removedby ydipping it into water to the desired depth. vThe.

body of cement containing the conductive material forms the center wire seals and also forms a part of the center electrode which conducts electrical charges from the binding post to the spark gap at the inner end of the plug'.

It is to be understood that the above detailed description of the present invention is intended to disclose an embodiment thereof to those skilled in the art, but that the invention is not to be construed as limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawing, since the invention is capable of being practiced and carried out in various ways without departing from the spirit of the invention. The language used in the specification relating to the operation and f unction of the elements of the invention is employed for purposes of description and not of limitation, and it is not intended to limit the scope of the following claims beyond the requirements of the prior art.

What is claimed:

1. A spark plug comprising a hollow ceramic insulator and a sectional electrode positioned in the insulator, a portion of said sectional electrode comprising a sealing body in said hollow insulator consisting of a compacted body. of a mixture of powdered insulating material and a conducting material interspersed therein.

2; A spark plug comprising a ceramic insulator having a central longitudinal bore, a sectional electrode positioned in the bore of the insulator, a central portion of the electrode holding a lower portion in position in the bore of the insulator, sealing the bore, said central portion comprising a compacted mixtureof powdered insulating material and powdered conducting material positioned in the bore to form a seal, being adapted to conduct electric discharges to the lower portion of the electrode. A

3. In insulators for spark plugs having a sectional central electrode, a section thereof cornprising a compacted mixture, of comminuted metal and a non-conducting compactible powder,

said section being cf 'mpacted in a bore oi the insulator to form a seal therefor.

4. In a spark plug, the combination of a ceramic insulator having a shouldered central bore, a sectional electrode positioned in the bore comprising at least one metal portionl positioned below the shoulder and adapted to project beyond the inner end of the insulator, and a second conducting portion positioned above the metal portion compacted in position in the bore of the insulator against the shoulder consisting oi a mixture of comminuted metal and a compactible non-conducting material, said second conducting portion holding the first portion in position and forming a close conducting relation therewith, and sealing the bore of the insulator against gas leakage.

5. In a spark plug, the combination of an insulator having ashouldered bore, a sectional electrode positioned in the bore, comprising a pair of met-a1 portions positioned at the ends of the bore connected ,by a compacted conducting portion consisting of a mixture of comminuted metal and a compactible non-conducting powder, said compacted portion of the electrode being positioned in the bore above the shoulder to seal the bore against gas leakage and to hold one metal'portion in position in the bore against the shoulder. f

6. In a spark plug, the combination of a ceramic insulator having a central bore, a sectional electrode positioned inthe bore comprising at least one metal portion, asecond portion of the electrode adapted to seal the bore consisting of a cement with conducting particles interspersed through the body of the cement in conducting relation with themetal portion whereby an electric currentmay be conducted through the sectional electrode.

7,'In a spark plug, the combination of a ceramic insulator having a shouldered central bore, a metallic electrode portion having a shoulder cooperating with the'shoulder in the central bore of the insulator, a cement body having a conducting powder interspersed in its body positioned above the metallic electrode portion and stopping the bore of the insulator to hold the electrode portion in position in the bore and to seal the bore, said cement body forming a part of a sectional electrode positioned in the bore'. whereby electric currents may be conducted through the cement body by the conducting powder interspersed therein to the metallic electrode portion.

8; In a spark plug, the combination of a ceramic insulator having a shouldered central bore, a sectional electrode positioned in the bore, comprising atleast one metal portion having'a shoulder cooperating with the shoulder in the central bore, a body of cement between the metal portion and the bore, and a sealing conducting mixture of at least two powdered materials having relatively Widely separated coefficients of expansion compacted in the bore over the terminus of the metal portion of the electrode to hold, the metal portion againstthe shoulder of the insulator and to have electrical contact therewith to form the sectional electrode.

9. In a spark plug, the combination of a ceramic insulator having a shouldered central bore, a sectional electrode positioned in the bore comprising vat least one metal portion adjacent the firing end of the insulator liaving a shoulder cooperating with the shoulder in the central bore, a body of cement adjacent the lshoulderpositioned between the metal portion and the bore to form a seal and a highly conductive heat path between the metal portion and the insulator, and

a sealing body in the bore comprising a mixture of a compactible non-conducting powder and a conducting powder compacted together to seal the bore in the insulator and in conducting relation with the metal portion to form a part of the sectional electrode. l

10. The combination set forth in claim 9 further characterized by an intimaterelation between the cement body and the compacted body, wherein the compacted body is placed in position while the cement is still wet.

ll. In a spark plug., the combination of a cef ramic insulator having properties similar to mulite or zircon, a shouldered central bore in the insulator extending longitudinally thereof, a sectional electrode positioned in the bore comprising, at least one metal portion adjacent the lry ing end of the insulator having a shoulder cooperating with the shoulder inthe bore of the insulator, a compacted body of a mixture of graphite and powdered talc positioned in the bore to form a sealing body and to hold the metal portion of' the electrode against the shoulder in the bore, said compacted body comprising from 20 to 96 per cent by weight of powdered talc and the balance graphite.

12. In a spark plug, the combination of an insulator having properties similar to that of corundum or magnesia, a. shouldered bore in the insulator extending longitudinally thereof, a sectional electrode positioned in the bore compris- 55 per cent by weight of powdered talc and the balance powdered copper.

13. In a spark plug, the combination oi a ceramic insulator havingy properties similar to mulite or zircon, a shouldered central bore extending longitudinally of the insulator, a sectional electrode positioned in the bore comprising, at least one metal portion positioned in part below the shoulder and adapted to project beyond the` end of the insulator, a second conducting portion of the sectional electrode 'positioned above the metal portion compacted in position in the bore of the insulator against the shoulder thereof consisting of a mixture of 'graphite and a compactable non-conducting powdered material, said second conducting portion holding the ilrst metal portion in position in the bore of the insulator and forming a conducting relation therewith and sealing the bore of the insulator against gas leakage and having an expansion coeillcient between 3.2 106 to 4.0X 10-6.

14. In a spark plug, the combination of a ceramic insulator having properties similar to corundum and magnesia, a shouldered central bore extending longitudinally of the insulator, a sectional electrode positioned in the bore comprising, at least one metal portion positioned in part below the shoulder and adapted to project beyond the end of the insulator, a second conducting portion of the sectional electrode positioned above -the metal portion compacted in position in the bore of the insulator against the shoulder ing, at least one metal portion adjacent the iiring,

end of the insulator having a shoulder cooperating with the shoulder inthe bore of the insulator, an intermediate compacted body of powydered copper and powdered talc to hold the metal portion of the electrode against the shoulder in the bore and to seal the bore against leakage, said compacted mixture comprising from 20 to thereof, consisting of a mixture of powdered metal and a compactable non-conducting powdered 'materiaL said second conducting portion holding the rst metal portion in position in the bore of the insulator and forming a conducting relation therewith and sealing the bore of the insulator against gas leakage and having4 an expansion coemcient between 9.6X10 to A CHESTER CIPRIANI.

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