US2672546A - Glow plug for compression-ignition engines - Google Patents

Description

7 Mam}! 1954 A. F. KLINGNER ET AL GLOW PLUG FOR COMPRESSION-IGNITION ENGINES Filed June 23, 1950 5111GT William H. Balentine Zhwcutor Add ph F. K1

I In I .4 .1 E F \v Gttorncg ifiioneuresistancez element fsh'oulid burni'outzithen-z Patented Mar. 16, 1954 PATENT: OFFICE? GLOW PLUG FOR COMPRESSION-IGNITION ENGINES r A'ildlpliFL "Klingner, and William H.. B'alentine;

Hellertown, Pai, ,assignors to Thomas A; Edison, Incorporated, West-Orange, N. J incorporation of N ew Jersey f ApplicationfJune 23; 1950; Serial No.- 169,810.,1

2 "Claims?" (Cl. 219-32) peraturerislnot raised highLenoughto assure com-t biistion. lfmcombustion fails; or .occurs late, de-w strncrtive pounding ,andhammering of fthBtWOBk 1 in tpartsimay occur ito-lcause serious damage to the engine. n

Glow plu s aresprovideduto overcome-this dif; ficulty., t These. plugs-5 "have .resistance n elements: which :are placedin:thercombustiomchamher'andi whichi amerheaited-v .byani electric-. storage battery; orzrthe likeqrtoaa fglowrf temperature'pwhichrrisea temperature'e'sufiiciently Jhigh: -..to :causeeignitiom; of theduel-21in:charges:- while -thesengi1 1e -:'is.,:cold. Although theseeresistance elementswire; so heat-e ecleelectricallyi-sonlyi during the" starting :period, a they have-to be; ab1e'- to e withstand the veryyhighi temperatures: in,the.:combustion.xrchambers;rand the heavy' engine. :-.vibration, encountered in; non-r: mal engine operation- Itzhasibeencommon, to make:the'resistanceielements Oil largei heavygwirerwhioh iszeapable ioi: withstandinguthesengine vibration andsthe corroe; sivemctionz'onthe hotweomhustionzxgasesnwithoutr supporlmor :novering rialong .=?:the1 i'.length3:thereofv Howevemsuch :iairgwtresistance rel'emehtsraretlob-i jectionablegfromx'a,z-sizeestandpointzzand. are: not usable:inrmanwoixthe.engines:ofimodern design; 5 Alsogrtheseelarget resistancewelements :zhavei had-a tCtfl) e: connenctedein iseries= to :conserve" the. current) dr'ain' ronrz themzbatterm Such-J.eseriesrzconnecting' isisvemmbjectionablesfmm ..theestalndpointzvthatz:

aliiofethe. glowmlugs; arezfdisablederi;

Iniorden to/meke' thesresistdnoe elements-relate Y tivelyysmalland \to provideithem with lsufiicientw' resistance 7 to/enable them-xto be-zconnectedLindi-L. 457 vidual-ly. acrossvthe; storage -rbattery'; int-parallel: with.ene.anothemz-theymust:he made of =relativzelyiva fine-theater wire. Such vfine, wire cannot with stand direct;.exposure to the combustion---gases-- hutemust be protectedubyra ,case. i Experience L angignition temperature, and which has yet'; ficient durability to withstand overfa. long DQIIOCI":

th'ejconstan't vibration, and the highheat -eiitl' corrosive action'of the combustion geses;'zen-" countered in modern compression-ignitionen ines.

Objects of the present invention are 'to provide design .and constructionimprovements in a glow plug of the type havingan'encasedheating'gel ment, which (improvements t enable the plug to" scription and theappended :cla'ims', reference bees;-

ing :had to the aocompanying'drawings, of which Figureal is a side view, 'pa.rtly.in elevation, and} partl$i in sectio'n" on 'a-iplane throughtthe central axis, of a glow plug according to our. invention Figure 2 ie an axial 'sectional '-view;="-to "larger? scale; of the lower' aotive= portionof -th'eqalugifof Figure 1; showingvaii'ious design and construe-E tio'n-details 'of the heating unitofth'e present plu'g according toour invention Figure 3 is a, 'cross'sectional-viewtaken' om-the' line '-3-"-3 of Figure?! but showing -'the= heating! unit with the ins'ulat-ing'fillerremoved: "and Figures4 end-'5 are end and-sideviews respec tively'of a locking bushing usedat the upper end of-tth'e' plug to' secure "the central spindle to the housing.

The glow plug showninFigure1 comprises an externally threadedshell I 0 having an axialbore l oar through which extends aisp'indle I I Inset; into the lower 'end'of'the bore Illa of theshell', against "an internal, shoulder 10b: and welded-to the shell at 'I 2, is a 1 heater-unit case l3"'havi ng 1a" heater winding 14 mount'edthereinp Theinn'er-" most end of the. coil 'is' "secured at fl 5 to theend' wall 'of the caiseiend the other endrof the: coil'issecured, at "5- to the adjacent endhf I'thespindle If. Thespindlelis centered axiallyinthe"shell,"v

. s'ulalting. washer I 1' at "itsv inner; end fanjd-ilhyfan".

insulating bushing it at its upper end. The washer I7 is mounted against a iiange IS on the spindle and is drawn against an annular shoulder 20 in the shell by tension exerted upwardly on the spindle, this tension being produced by threading a nut 2| on the outer end portion of the spindle against the bushing l8. The bushing I8 is centered relative to the shell by having a tapered end portion 22 which fits into an outwardly-flared end portion 23 of the bore Inc in the shell. On the outer end of the spindle there is a knurled hand nut 24 for clamping a lead wire (not shown) between it and the nut 2 I.

The glow plug is mounted by threading the shell I 0 into an internally-threaded opening provided in the cylinder head of the engine, the plug being threaded inwardly until the heater unit thereof is exposed to the combustion gases in the precombustion chamber of the respective cylinder of the engine. for the plug is completed by connecting the spindle H to one terminal of the ignition battery by means of a lead wire (not shown), and by making a ground connection between the other terminal of the battery and the case 13 by way of the cylinder head and shell 10, it being herein unnecessary to show the engine parts referred to since the means of mounting the plug and of making its circuit connections are well understood.

If the engine is cold, the energizing or heater circuit of the plug is closed to heat the case I3 to a glow temperature before the engine is cranked. When the case is so heated, it will supply sufficient heat in the respective combustion chamber to compensate for the heat loss to the surrounding combustion chamber walls, and will assure ignition of the respective fuel-air charge as this charge is compressed. One such plug is provided for each cylinder so as to assure even starting and running of the engine during the warm-upperiod. When the engine has warmed up, the heating current to the plugs is out 0115, but inasmuch as the heating units of the plugs are in the combustion chamber and are subjected continuously to the high temperature, corrosive action and pressure of the combustion gases, as well as to the vibration of the engine, so long as the engine is running, the plugs must be of very durable construction.

A first specific requirement of the present glow plug is that the case 13 be able to withstand the high temperature, corrosive action and pressure of the combustion gases in the engine cylinder. That this is a stringent requirement will be appreciated when it is realized that the case cannot have good heat conduction lengthwise thereof else the heater coil in the case will beunable to heat the case to the required temperature. Since thecase must have poor heat conduction to the shell to which it is secured, it will acquire nearly the temperature of the combustion gases, and will be thus at a much higher temperature during normal engineoperation than will be the surrounding combustion chamber walls which are cooled by water jackets, air flow, etc. A low heat conduction lengthwise of the case, together with an ability to withstand the high gas pressure in the engine cylinders, requires a case wall thickness of the order of .032". Extensive tests have shown that a case cast to shape is far more satisfactory than one machined from solid bar stock because a cast case has a tougher grain structure and is more resistant to corrosion. It is found that suitable alloys for the case comprise The energizing circuit iron, cobalt, nickel, chromium, tungsten and carbon as basic ingredients and that certain improved properties are obtained when such alloys contain minor percentagesi. e., about 3% or lessof one or more of the ingredients: molybdenum, columbium and nitrogen. A highly-preferred material for the case is Haynes Stellite Multimet alloy, designated N-l55, the composition of which is: 0.30-0.40 C; 18.0-22.5 Cr; 18.0- 22.0 Ni; 2.75-3.75 Mo; 0.75-1.50 Cb; 2.0-3.0 W; 18.0-22.0 Co; 0.10-0.20 N and balance Fe. Extensive tests have shown that this alloy is highly resistant to oxidation at temperatures up to 2000 F. and is highly resistant to acid attack by the fuel combustion products. Also, it has high strength at high temperatures making it suitable to withstand the compression pressures and temperatures inherent in the cylinders of diesel engines.

In order that the glow plug will positively initiate ignition when the engine is cold, the heater winding M must be capable of heating the case l3 to a glow temperature of the order of 1840 F. Since the melting temperature of available heater wire is only a few hundred degrees higher than this temperature, it follows that good heat conduction is required between the winding and the case; yet, it is also required that the heater winding be electrically insulated from the case. These conditions have been met by lining the inner peripheral wall of the case 3 with a thin tubing of mice having the length of the case and a diameter such that it will just fit snugly into the case. This mica tubing is made of sheet stock of the order of .001 thick wound into tubular form to a wall thickness of the order of .005" to .007. The thickness of the tubing is very critical since it is found that thicknesses of less than .005" are not durable enough to withstand the engine vibration for the required life of 1000 hours under the extreme heat conditions encountered in normal engine operation. On the other hand, thicknesses substantially greater than .007", say 0.01 or more, will cause the heat conduction between the heater coil and'the case to be so reduced as to make it impossible to heat the case to the required temperature.

When the heater unit is small and the heater coil is to work from the full voltage of' an automotive storage battery, the typical voltage of which for diesel engines-is 12 volts, the heater wire must be very thin and must be supported firmly in the case so that the engine vibration will not loosen it and cause shorts or opens to develop. Typical present-day sizes of the heater case l3 are 1%" to outside diameter and 1" to 1 length. To heat the case to the desired glow temperature above mentioned, from a voltage source of 12 volts, approximately 72 watts of electrical power must be expended in the heater winding and the winding must have approximately 2 ohms resistance. These requirements have been met satisfactorily by using a heater coil having of the order of 20 turns of No. 23

wire wound in a cylindrical helix of about length, with even spacing between successive turns. The diameter of the coil is made such that the coil will just flt easily into the mica tubing which lines the inside wall of the case. Even spacing between turns and easy fitting into the case are very important so that when the winding is installed, the spacing between the terminals and the inner end portion of the heater coil will not be reduced to cause possible shortingbtween turns with resultant burn-outand shbrtenin'g of life.---

-abovementioned;- the innenend of"'th'e heatercoil is connected at llito the endwall of disease so as-to-complete the'electric circuit of the-heater coilby way, of the case and" shell of the. glow plug: Thisjointbetween the coil and case 'is very critical: It must'be' a mechanically strbngijointto withstand the-intense heat and vibration of--the'-'engine;- and-it must be 'alowresistancejointso that the heating current will not'here produce'a -hotspot and cause burn out and shorteningcofrlife': To meet these requirements satisfactorily,-a bead 2? preferably. of

stainless steel which is. for. instance globular or tu'biila'r in shape, a tubular shape being preferred,- and being shown in Figure 3, is threaded -onto the inner end of the coil, and this inner end is bent inwardly substantially on a diameter line of the coil so that the head is centered at the axis of the coil and lies against the end wall of the case after the coil is installed. A spot-welding electrode (not shown) is then inserted into the case against this bead and is fed a timed. impulse of heavy current to weld the bead simultaneously to the wire and to the end wall of the case. At this stage in the assembly operation, the end lead wire 26 of the heater coil, at the outer end of the case, is extended outwardly along the wall of the case so as not to obstruct access to 30 the interior of the coil. Preferably, the welding electrode is provided with a concave end face so that it will impart an oval shape to the bead (Figure 2) during the welding operation. This manner of forming the joint Iii between the heater coil and the case is important in realizing the durability of construction required to obtain the desired life under the stringent conditions in which the glow plug is operated.

in place in the case, and to afford good heat con- In order to hold the heater-coil turns firmly in place in the case, and to afford good heat conduction between the turns and the mica insulation lining the case, a layer 25 of chemicallysetting ceramic cement is placed between the turns and onto the insulating tubing after the coil is inserted. This allows the cement to be installed easily as by means of a small brush. Preferably, a quick-drying cement is used. A suitable cement comprises aluminum oxide mixed with quick-drying agents of magnesium fiuosilicats and sodium silicate and is available commercially as Sauereisen Cement No. 21. This cement bonds the coil turns firmly in the mica tubing, has good heat conduction and is able to withstand the intense heat to which the heater unit of the glow plug is subjected.

After the heater coil is welded to the case and the coil is cemented in place in the manner above described, the inner space of the coil is filled so with a powdered ceramic insulation 28, preferably of an alkaline metal earth compound such as aluminum oxide. This powder is tamped firmly into the case to a level suitably beyond the outer end of the coil but not so as to completely fill the case. The outer lead wire is then bent so as to extend axially out of the case as shown by full lines in Figure 2, and the remaining end space of the case is filled with ceramic cement 29 which may be a cement such as the cement 25 hereinbefore described. The next step in the construction of the present glow plug is to make the joint [6 between the outer lead wire it of the heater coil and the spindle N. This joint is made by inserting the wire 26 into an axial opening in the spindle and thereaften-tiweldinginterim place. It" is important athat sthe. dead *wirezzZB have aslack length betweenuthe spindle and the.. case so that 'tensionwhich may be exertedionr the spindle -will not put "strain: on thev .heater coilassembly to dislodge' or lo'osenit. inzthe case:v This slack is 1 provided: by givingflthetlead .nwire a kink 30 as shown-:in Figure 2.

After the stepjust'.rdescribed is completed, the spindle is threaded through the shell and the-case is fitted into the end of the shell and welded thereto as aforementioned. Next, the spindle istightened into place by threading ,the. nut 2| tightly against the bushing l8... lnithis tightening operation, it'is'important marsh-e spindle be held firmly against being turnedrelaitive to the shell"'so as to prevent torsional strain from being exerted on the lead wire 26. For this purpose the bushing I8 is slotted lengthwise at 3| (Figures 4 and 5) so that the initial forcing of the tapered end of the bushing into the flared opening of the shell will compress the bushing tightly against the spindle and hold the latter from turning relative to the bushing.

Although the glow plug of the present invention is particularly adapted for use in the pr-ecombustion chambers of diesel engines, it will be understood that the present plug may have many other applications. Accordingly, no unnecessary limitation to use in engines is intended by the reference in the preamble of the claims to an engine combustion chamber.

The foregoing description is intended to be illustrative and not limitative of our invention since the glow plug herein particularly shown and described, while being a preferred embodiment, is subject to changes and modifications without departure from the scope of our invention, which we endeavor to express according to the following claims.

We claim:

1. A glow plug for use in an engine combustion chamber comprising a cylindrical resistance coil, a cylindrical protective case for said coil, and a tubing of insulation lining the interior peripheral wall of said case for effectively insulating the coil from the case along the length of the coil without materially decreasing the thermal conductivity between the coil and the case, said insulating tubing comprising a sheet of mica of approximately .001" thickness wound several turns on itself into tubular form to a wall thickness between .005" and .007", and said coil having a normal diameter slightly less than the inside diameter of said tubing to permit the coil to be inserted slidably into the tubing without longitudinal displacement of the turns of the coil relative to each other.

2. A glow plug for use in an engine combustion chamber comprising a metal cylindrical case having a wall at one end, a tubing of electrical insulation lining the inside peripheral wall of said case and comprising a sheet of heat resistant insulating material of the order of .001 thickness wound several turns on itself to a wall thickness of the order of .005" to .007", a cylindrical resistance coil in said case having a spacing between adjacent turns thereof, the inner end portion of said coil in said case being bent along a diameter line of the coil to form a lead wire adjacent the end wall of the case and said coil having a normal outside diameter slightly less than the inside diameter of said tubing to permit the coil to be slid into the tubing without longitudinal displacement of the turns relative to each other.

a; metal bead on said lead wire in a position substantially at the axis of the coil and welded along said axis both to the lead wire and to said end Wall, and an insulating cement in said case between adjacent turns of said coil and in bonded relation with said insulating tubing for holding the turns of the coil permanently in place.

ADOLPH F. KLINGNER.

WILLIAM H. BALENTINE.

Referenees Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,457,690 Brine June 5, 1923 1,463,855 'lartrais Aug. '7, 1 23 1,609,688 Briggs Dec. 7, 1926 OTHER REFERENCES Metals Handbook, 1948 ed., pp. 5'78, 579, 580; published by the American Society for Metals Cleveland 3, Ohio.

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