US1987024A - Spark plug - Google Patents

Description

Jan. 8, 1935. J. w. PARKIN. SR

SPARK PLUG Original Filed Feb. 20, 1930 2 Sheets-Sheet l Jan.8,l935.

J. W. PARKIN, SR

SPARK PLUG 2 Sheets-Sheet 2 Original Filed Feb. 20, 1930 Patented Jan. 8, 1935 UNITED STATES.

PATENT OFFICE Application February 20, 1930, Serial No. 430,061 Renewed May 28, 1934 1 Claim.

This. invention relates to spark plugs, and. proposes a novel construction based strictly upon scientific and engineering principles for adapting the plug to the varying conditions of internal working temperature incident to engines of different compression pressure in which the plug may be employed; for enabling the exposed parts of the plug to withstand sudden temperature changes such as are encountered in aeroplane practice; for ensuring the plug against beingcontributory to detonation in the cylinder; for improving the sealing of the plug parts against compression leakage; for promoting the passage of the spark, particularly in engines of high compression; and for facilitating the manufacture, assemblage, and the selection. and provision of the proper plug for a particular .use.

One of the objects of the invention is to provide a spark plugwhi'ch by the simple interchange of a gasket may be adapted for high, medium, or low compression internal combustion engines, thus obviating the need of supplying special spark plugs for each type. of engine.

Another object of the invention is the provision of a shield for the exposedportion of the porcelain, so disposed and'secured that the pressure thrust of the shield retaining means is transmitted solely through the central portion; of the shield, whereby breaking strains from. the center to the periphery ofv the shield are avoided.

A vfurther object of the-inventionis to construct the walls of the flame chamber at the mouth of the plug in such. manner as to secure maximum heat conductivityas well as to protect the ionized spark path between the electrodes, against. deflection, by setting: up a succession of opposing counter tides to the'inflow of the mixture under the stress of the compression stroke, thereby maintaining the body of mixture in the immediate vicinity of the sparking terminals substantially inert.

Still another object of the invention is the provision of sunken seats for the gaskets supporting the insulator, so that the gaskets, once placed, be-

come retained in the bushing and, ring-nut respectively, ensuring the correct seating and centering of the porcelain each time it may be removed and replaced, as well as enhancing the sealing efliciency of the gaskets by lengthening the contact surface between said gaskets and the parts which embrace them.

With these and other objects in view the. invention is, disclosed in the following specification and the accompanying drawings in which the same characters of reference employed throughout the several figures to denote identical parts.

In the drawings,

Fig. 1 is a view partly in elevation and partly in section showing a spark plug embracing features of the invention and particularly designed fora high compression engine.

Fig. 2 is a longitudinal section through the plug showing a slightly larger gasket between the porcelain and bushing, adapting the plug to an engine of lower compression.

Fig. 3 is a, bottom plan view of the spark plug.

Fig. 4 is a cross section taken along the line 4-4 of Fig. 2, looking downward. v

Fig. 5 is a longitudinal section through the same plug, a thick gasket being used, greatly enlarging the combustion space around the insulator, the arrangement being particularly designed for a low compression engine.

Fig. 6 is a longitudinal section of an intermediate portion of the spark plug showing a slight modification in the mode and means for seating the gaskets, it being understood that the other features of the plug may be the same as shown in Figs. 1, 2 and 5.

Fig. '7 is a cross section taken along the line 7-7 of Fig. 6, looking downward, the porcelain and gasket being removed.

" Fig. 8 is a longitudinal section of the lower end of the ring-nut shown in Fig. 6, the gasket being omitted.

Before referring in detail to the several figures it may be stated as a matter of known and recognized fact that the higher the compression of an engine, the higher is the heat value generated at the time of explosion. An ordinary spark plug which may work well in a low compression engine will therefore fail to work properly in a high compression engine due to the fact that it becomes overheated at the explosion temperature of high'compression causing detonation or preignitlon of the charge.

'On the other hand, while it is highly desirable that the plug should be so designed and constructed as to be free from overheating yet it is essential that it be capable of being heated to the extent that carbon deposits shall not condense upon the insulator.

With regard to overheating of the porcelain it is idle to propose conducting the heat away from the porcelain for the insulator is at best a poor conductor of heat and no matter how much metal may be made to contact with the insulator with a view to promoting the dissipation of heat therefrom, this will relieve the superheated condition of those surface areas only, with which the metal makes intimate contact and the cooling of the porcelain by such means is practically negligible. The only way in which the porcelain can be effectively prevented from becoming overheated is to control the access to it of the heated gases of explosion.

Now adverting to Figs. 1, 2 and 5, the bushing is represented by the reference numeral-'1, in which the insulator 2 is disposed between gaskets 3 and 4 and held in place by a ring-nut 5 screwing into the bushing into compressive relation to the gaskets and the shouldered zone of the insulator. It will be noted that in all three of sulator tapers as indicated at 6 and that this tapered portion is surrounded by a wall '7 of the bushing having a corresponding taper so that the sides of these corresponding portions ofthe bushing and insulator lie parallel and slightly spaced. In Fig. l the gasket 3 is quite thin, determining a narrow annular combustion space between the insulator and bushing. This not only minimizes the combustion chamber of the cylinder but at the same time it restricts access of the heated gases of explosion to the surface of the insulator so' that a'minimum of heat is imparted to the insulator. This plug is therefore adapted to an engine of high compression and detonation is avoided by exclusion of the heated gases from the porcelain to the extent that said porcelain shall not become heated to the ignition temperature of the compressed mixture. Fig. 2 shows the same bushing 1, the same porcelain 2 and'the same portions 6 and '7 of corresponding taper. In this plug the thin gasket 3 has been replaced by a thicker gasket 8 and in consequence of this substitution, the annular space between the tapered portions of the insulator and bushing is considerably wider than the annular space in Fig. 1. This effect is brought about solely by using a different gasket, and the result is not only to slightly increase the combustion chamber of the engine, thus determining a lower compression pressure, but to admit a larger volume of the heated explosion gases and thereby permitting the insulator to become more highly heated than is possible in Fig. 1. A lower cylinder compression can stand a hotter spark plug without risk of detonation of the mixture, and a hotter spark plug is desirable in order to prevent the condensation of carbon upon the insulator.

. Fig. 5 shows'the same plug parts as Figs. 1 and 2 with the exception that a still thicker gasket 9 has been employed between the porcelain and bushing so that the annular space between the tapered portions 6 and 7 of. the porcelain and bushing respectively is now quite wide, adding materially to the volume of the combustion chamber and at the same time admitting a pracferent size according to the prescribed degree of compression in connection with which the plug is to be employed. This has necessitated the turning out of plugs with different sized bushings from the factory, and the maintaining of stocks of these dilferently sized plugs by the dealer. The present invention secures the same result with identical bushings for spark plugs adapted for every grade of compression, merely substituting a difierent gasket, suitable to produce the desired result, in the assembling of the plug. This minimizes the number of difierent parts which the factory must-turnout in producing its complete lineof sparkplugs and it materially reduces the stock which the'dealer must carry in order to be completely equipped,

for to change from a plug of one compression to that of another it is only necessary that the the aforesaid figures the lower portion of the in-,,

dealer disassemble the plug he may have on hand, replace it with asuitable thicker or thinner gasketfas the case may be, and thus produce a spark plug exactly adapted for the required pur- P Se.

In order further to eliminate the possibility of detonation through-the overheating of the spark plug that part oithe bushing l which threads into thecylinder aperture is made as massive as possible, and provided with heat diffusing ridges 10 in the mouth of the flame chamber said ridges decreasing in diameter toward the sparking terminals so as to give a general outward flare to the flame chamber. Said ridges'are preferably acute at their edges andof progressively increasing thickness so that the heat conductive capacity of said ridges increases progressively toward the massive part of the bushing, from which bushing the heat is carriedaway through the cylinder walls and through the cooling medium in the water jacket provided that the engine is of the liquid cooled type;

The ridges 10 also perform an important function in preventing disturbance of the spark path between thelectrodes. It is well known that a brush discharge immediately precedes the passage of the spark,'- which brush discharge ionizes the gas between the terminals decreasing the resistance and making it ea'sierfor the spark to jump :the gapp'It isknow'n also that the ionized gas can readily beblo-wn out of its rectilinear path, causing arcing of the spark. This increases the length of the sp'ark'gap and requires a current of greater voltage to jump the gap. When the tidal flow of mixture, urged by the compression movement of the engine piston sets in toward the spark plug, the mixture impinges against'the ridges, setting up concentric eddies or counter-tides which buck the infiowing mixture,.reducing the flow velocity of said mixture and/maintaining the restricted body of mixture in the immediate vicinity of the sparking'termi nals inert, so'that the spark isnot blown into an are but passes substantially rectilinearly, thus requiring a lower voltage than under ordinary conditions. This is extremely important since it is well known that the resistance of the gap increases and becomes quite enormous in highly compressed mixture.

The gaskets 3, 8 and 9 upon which the insulators are supported in the several adaptations of the invention, aswell as the gaskets 4 which seal the joint between theporcelain and the ring-nut are preferably formed of malleable metal such as copperand as shown in Fig. 6 it is preferred to seat them in shallowannular channels. 12 and 13 formed on the confronting shoulders of the bushing and ring-nut respectively. When the gaskets are first put in place and the ring-nut is screwed tight, the gaskets are spread sufficiently to give them a retaining lit in the channels in which they are seated. This prevents the gaskets becoming displaced when the ring-nut and insulator are removed from the bushing, so that upon replacement of the insulator it will always be correctly seated and centered. The arrangement of the gaskets within the annular channels also improves the sealing property of the gaskets by lengthening the area of contact between the gaskets and the bushing and ring-nut respectively. It is of course to be understood that the pressure of the ring-nut upon the gaskets conforms them against the insulator in such manner as to produce a perfect and gas-tight seal between said gaskets and insulator.

In order to adapt the spark plug for aeroplane use it is essential that the portion of the insulator exposed to the atmosphere must be protected against sudden temperature changes. In making a dive from high altitude with throttle closed the heated porcelain is suddenly subjected to a temperature drop bringing it down to zero within a few seconds. Contraction stresses are produced by this sudden cooling which commonly cause fracture of the insulator. By the present invention, the exposed end 14 of the insulator is protected by a shield of insulation material 15, preferably porcelain. This shield surrounds the central electrode 16 and has a shoulder abutting the upper face of the ring-nut, a gasket 17 intervening. The shield 15 is spaced from the insulator and in consequence does not become materially heated. Therefore under conditions of sudden temperature change such as have just been related it is not subjected to the injurious strains due to sudden cooling. A nut 18 bears against the upper end of the shield 15 for holding the latter in place. If the pressure of the nut were transmitted through the shield to the peripheral edge thereof which rests adjacent the upper face of the ring-nut, breaking stresses might be set up in the material of the shield. In order to prevent this a gasket 19 is placed between the top of the shield and the upper end of the insulator the relation of which to the gasket 17 is such that when the nut 18 is tightened the pressure thrust is transmitted directly through the central portion of the shield to the upper end of the insulator so that it may be correctly said that the shield rests and is retained upon the upper end of the insulator and not upon the upper end of the ring-nut. The gasket 17 between the peripheral edge of the shield and the ring-nut serves solely as a packing to prevent access of the outside atmosphere to the outer end of the insulator. A packing gasket 20 may be arranged in an annular space at the upper end of the shield beneath the nut 18 and surrounding the central electrode. According to approved practice, the central electrode is riveted over the nut 18 as indicated at 21 in Fig. 2 to prevent dislodgment of the insulator.

While I have in the above description disclosed what I believe to be a preferred and practical embodiment of my invention it is to be understood that the specific details of construction are merely by way of example and not to be considered as necessarily limiting the scope of the invention.

What I claim as my invention is:

In a spark plug a bushing having a portion of general hour-glass shape having bores tapering from both ends toward an intermediate constricted portion, an insulator seated in said bushing having a portion tapered corresponding to one of said bores and extending thereinto, forming an annular combustion space, the opposite bore being formed with a series of annular parallel ledges facing away from said combustion space and a progressively diminishing diameter toward the constricted part of said bushing forming edges lying in the surface of an imaginary cone, tapering towards the interior of the plug. L

JOSEPH W. PARKIN, SR.

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