US2024387A - Glow plug - Google Patents

Description

Dec. 17, 1935. H. RABEzzANA GLOW PLUG Filed July 21, 1952 Patented Dec. 17, i935 GLOW PLUG Hector Flint, Mich., saigner, b

mesne assignments, to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application July 21, 1932, serian No. 623,710

2 claims. (c1. 12s- 145) This invention relates to ignition devices for internal combustion engines and particularly to glow plugs for use with the .compression ignition itype of engine.

As an aid to starting, engines are sometimes equipped with a plug extending through the combustion chamber wall and carrying a resistance wire which can be heated to incandescence by the passage therethrough .of electric current of rela- -tively low voltage. Because of the low voltage and the conditions to which the plug is subjected, it has been dimcult to produce a plug which will stand up and give satisfactory service for any appreciable length oi time. The intense heat of combustion and the chemical changes that take place in an engine combustion chamber cause oxidation and corrosion of the wire which destroys the electrical contact between the ends of the wire and the parts to which the wire is connected. vTo avoid troubles of this sort, it is hereproposed to fasten the ends of the resistance wire at as cool a spot possible and beyond the zone of greatest heat and to protect the contact against excessive oxidation.

A construction to accomplish this purpose is illustrated in the accompanying drawing wherein optional plug structures are shown in the scctional views, Figures 1, 2, and 3.

Referring tothe drawing, the plug shown in Figure 1 includes inner and outer metallic members I and 2, respectively, suitably insulated Afrom one another. The outer member or shell 2 is here shown as provided with a hexagonal head 3 for engagement by a wrench to facilitate installation and removal of the plug, and with a dependent screw threaded skirt I adapted for engagement with a screw threaded opening in the wall of the engine through which it is grounded. Interposed between the inner and outer members for insulation purposes is a tube 5 of mica or the like and upper and lower bodies of mica washers E and 1. seated at opposite ends against an enlarged head 8 on the lower end of the central rod I and against a sleeve 9 of brass, copper or other ductile metal, while the upper body 6 rests against the top surface of the head 3 and the undersurface of a coupling or terminal nut I threaded or otherwise fastened on the upper end of the central member and adapted for connection with the usual ignition cable. To hold the parts in assembly and prevent leakage therethrough, the outer shell, at the time of assembly, may be heated at an intermediate portion and placed under axial pressure to collapse the same and The lower mica body 1 is cause an inward bulge as at II', which deforms the sleeve 9 and through the sleeve exerts an inward compression of the mica tube 5, whereby the tube tightly hugs the adjacent portion of the central rod I.

The inner and outer metallic members' I and-2 carry a suitable glow wire or resistance element at the lower end of the assembly, the intermediate portion of which is shown in the form of a helical coil I2 with one end portion' I3 turned upwardly and projected into an opening ir the bottom of the skirt, extending upwardly into the body of the shell and preferably beyond the skirt portion engaged by the wall of the combustion chamber. At its upper end,` as at Il, the porl5' tion I3 enclosed within the skirt, is staked, welded, or otherwise secured tothe shellv for the purpose of making an electrical contact therewith. The opposite end portion I5 extendsup-l wardly through an opening in the central rod I and at its extremity is secured to either the member I or to the terminal connector III by silver solder, staking or the like. for contact purposes. It will be seen, therefore, that both ends of the resistance wire'are electrically connected to their 25 respective connector portions at points consider'- ably removed from the hot end of the plug and are saved from eiIects of the intense heat and protected against oxidation.

The plug heretofore describedwill be found suitable for use with a six volt ignition system, but for those systems where the -voltage is higher, for example in the neighborhood of twelve volts, the diameter of the resistance wire must be materially reduced and in order to give proper support for the wire it is proposed to mount the exposed portion on the lower end of the central member as shown in Figure 2. In this gure, the inner and outer metal parts I1 and I8 are insulated from each other by mica or 40 an equivalent tube I9, and are held together by the thermoplastic collapse of the restricted neck 20 of the shell I8, which deforms a ductlle sleeve 2| to seal the parts-and transmit the deformation pressure to the mica tube. The lower portion of the central rod I'I, which projects beyond the-bottom of the skirt, may be provided with a helical groove in which is seated the coil 2l of the resistance wire, one end of which projects up through the member I1 and is secured at 24 50 at the top with the other end projecting upwardly through the skirt of the outer member I8 and being secured thereto as at 25.

In this particular construction, an enamel or an oxidized coating is provided on the'exposed 55 surface of the central rod I1 and below the insulator tube IS, to assist in the insulation of the inner and outer metal members from each other.V

Obviously such coating insulates adjacent turns 5 of the glow wire coiled upon the rod. It may even be found practical for some uses to coat the entire outer surface of the central rod and entirely eliminate the need for the separate insulator sleeve i9. m A porcelain core insulator is. illustrated in Figure 3 where the core is formed in two pieces 21 and 23, respectively. The outer shell 29 in this case is provided with an internal shoulder 3l at its lower'end forming a seat for a gasket 3| and the base of the insulator 21. It is also provided with a flange or lip 32 which may be pressed or spun inwardly over a gasket 33 seated on the upper end of the core 21. 'I'he lower insulator sleeve 28 bears at opposite ends against thebottomofthecore 21andanenlargedhead 3l at the lower end of the central rod 35, which projects upwardly through the core 21 and carries at its upper end a coupling nut 36. The bottom of the nut 36 is preferably provided with 25 a dependent skirt 31 which encloses a sealing gasket 33 and a washer 38 interposed between the nut and the core 21. The resistance coil Ill in this case is wound about and seated on the sleeve 28 with its opposite ends extending 30 through and connected to the inner and outer members as before described. In this connection the two part insulator is important because of the tremendous difference of temperature existing between the lower end of the plus and theupperend. Ifthecoreweretobemadein a single piece, the temperature dinerence would cause it to crack. However, by providing a separate insulator sleeve at the lower end, crackling iseliminatedbecausethisbodyissubjectedto a somewhat uniform temperature throughout its mass, and furthermore, it can be of a diiferent composition from that of the main core body, and be selected because of its ability to withstand high temperatures. 0n the other hand, 5 the material in the main core only needs to be suitable for taking the pressure exerted upon it between the seat 38 and pressed in flange 32.

l. A glow plug for use with compression ignim tion engines and adapted to be secured in an aperture in the wall of the combustion chamber comprising a central member having a substan tially axially extending bore therein of uniform diameter from end tb end, an outer shell having l5 a skirt portion to be secured in said wall and being provided with a bore of uniform diameter extending upwardly beyond the portion to be received in the wall, and a glow wire having a portion of its length intermediate its ends ex- 20 posed within the combustion chamber with the upwardly extending ends thereof completely lilling the respective bores before mentioned and connected with both the central member and the shell outside the wall of the combustion 25 chamber when the plug is in operating position.

2. In a glow plug, an outer shell, an insulator core mounted in said shell, a central spindle having its lower end projecting beyond the core and terminating in an enlarged head, an ex- 30 posed sleeve fitted to the projecting spindle end between said head and the bottom of the core, and composed of insulating material having heat resistance properties diiferent from the material of said insulator core, and a glow wire connec- 35 tion between the spindle and shell, having an intermediate portion coiled upon and suppOrted by said insulating sleeve.

HECTOR RABEZZANA.

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