US2269682A

US2269682A - Spark plug

Info

Publication number: US2269682A
Application number: US340659A
Authority: US
Inventors: George M Paulson
Original assignee: Individual
Current assignee: Individual
Priority date: 1940-06-15
Filing date: 1940-06-15
Publication date: 1942-01-13
Anticipated expiration: 1959-01-13

Description

'Jgm 13, 1942. G. M. PAuLsoN SPARK PLUG Fi1ed June.15, 1940 2 sheets-sheet 1 www.. 2%0

1 'AL/nh ATTORNEY Jam.l 13, 1942. I G. M7 PAULsoN 2,259,532

' SPARK'PLUG l Filed June 15, 1940' 2 sheets-sheet 2 6291i; 7a. ,al1-ara- INVENTOR ATTORNEY -tageously follow tures of the surrounding gases in the engine, and 30 Patented `lan. 13, 1942 UNITED STATES ATENT `OFFECE SPARK PLUG G ieox'ge M. Paulson, New York, N. Y. Application June 15, 1940, Serial No. 340,659

(el. 12a-169) 1'1 Claims.

One object of theinvention is to provide an electrode construction which can operate for as,

greatly longer period without gap setting than do the constructions heretofore known, and which is capable'of such extended service under the extreme conditions'met'with in aviation en- Another object of the invention is to provide a construction which permits much` closer spacing of the electrodes than has previously been practicable.

The shorter spark gap, ing voltage requirement, brings the total ignition requirements Well within the limits of the magneto output capacity in shielded ignition systems, and enables the plugs to operate satisfactorily, with high density charge at the time of ignition resulting from hi'gh boost pressures or high compression ratios. The reduced sparking voltage gives lower electrical gradients throughout the entireignition system, resulting in much less danger of insulation failure and other electrica1 phenomena which accompany high electrical gradients.

Another object of electrodes, the temperatures of whichv advanor approximate -the temperawhichare cooled largely by radiation -and Aby surface contact with gases, and which do not, or need not, depend, for cooling, upon the conduction of heat from the ground electrode to the shell body, or from thecenter electrode to the 35 spindle head or spindle.

Itis a feature 'of the invention that the electrodes are of small mass, and of considerable total surface area in relation to their mass. The path for heat electrodes from the spark gap to the massive parts of the plug is preferably relatively long and of small cross-section in order to maintain high electrode temperatures when the. engine is rst plug are cold.

The electrodes of this invention operate at higher temperatures at the time of occurrence of the spark, in starting and under light loads, than is the case with massive electrodes. operating temperature of the electrodes under these conditions causes the gas in the gap between the electrodes to be of comparatively low density and results in lower break-down voltage of the gap. one

by'reducing the sparkinvention are made of the invention is to provide transfer through the metal of the the lower end of a. modied The higher including a sleeve II factor that reduces wear plug. A compressible gasket on the electrodes, and in combination with the diminished gap and the special electrode construction it enables spark-plugs embodying this invention to perform longer under more adverse 4conditions than has yet been possible.

The higher electrode temperatures and a perforate construction of the electrodes obvate any tendency to quenching of the ignition spark on starting or during operation under light load, and

make feasible the use of shorter gaps.

The electrodes of spark-plugs embodying this' metal that is of high melting point and resistant to corrosive gases, preferably rare metal alloys.

It is -another object of the invention to provide an electrode construction that requires only small amounts of expensive rare metal, but which obtains large surface 'area and mechanical rigidty.

Other objects, features and advantages of the invention will appearor be pointed out as the specication proceeds.

In the accompanying drawings, forming part hereof:

Fig. 1 is a side view elevation but with the tion.

of a spark-plug, mostly in Fig. 2 is an end view of the spark-plug shown in Fig. 1.

Fig. 3 is an enlarged side elevation of the center electrode, showing its connection with the spindle.

Figs. 4 and 5 are an enlarged side elevation and an enlarged bottom plan view, respectively, of the ground electrode when not connected to' the spark-plug shell.

Fig. 6 shows another construction that can be used in place of the spindle shown in Fig. 1.

Fig. '7' is an enlarged sectional view, showing form of the invention` Fig. 8 is an end view of the spark-plug shown in Fig. 7.

Fig. 9 is an Fig. 10 is an end view of the spark-plug shown in Fig. 9. A

Fig. 1 shows the invention in a spark-plug having a central spindle I2. This insulation .is die, and the spindle is held in a core nut I3..

The core nut that screws into the body or shell- I6 .of the spark- I8 clamped between enlarged sectional view, showing a started and thewiarge, non-sparking parts of the 45 second modified form of the invention.

I3 has ya threaded extension IQ-4 lower part shown in sec- I0 surrounded by insulationv of mica and mica washers clamped againstfthe spinthe core nut I3 and the upper end of the shell I6 makes the spark-plug gas tight, and permits adjustment of the electrodes (gap setting) by controlling the extent to which the core nut I3 is screwed into the shell I6.

A center electrode 20 is attached to spindle. This electrode 20 is made of extremely thingauge sheet metal and is a grill or perforate element with radial bars 2| (Fig. 3) connected by

rings

22, 23. Above the upper ring 22 there are l0v legs or supports 24 that extend straight up to the head of the spindle IIJ. and each of these supports 24 is welded or otherwise united to the lower end of the spindle head.

The lower part of the grill including the outer surfaces of the bars 2| and the

rings

22, 23 comprise the sparking surface of the electrode, and the legs or supports 24 may be made long in order to increase the length of the path that mustjbe traversed by the heat in passing from the sparking surface to the spindle I0, which is of greatl mass in comparison with the electrode grill.

The grill from the upper ring 22 down is frustoconical. In the preferred embodiment ofyfthe invention the center electrode 20 is stamped tout possible by the fact that the electrodes are of small mass in relation to their surface areas, and of grill construction. With massive electrodes, small gaps such as are made possible with this invention are not practical because they make the engine performance at starting and under light loads unsatisfactory. The reason for this difference in result is probably that the gas close to the electrodes is chilled by thick electrodes even though the compressed gas in the cylinder may be at a high temperature, and that the chilling effect of the heavy electrodes, when very close together, quenches or prevents the ignition of the charge.

With this invention the small mass of the electrodes in relation to their surfaces of contact with the gases .in an engine cylinder causes them of sheet metal as a single piece, and is made of' platinum alloy. 10%-20% rhodium platinum or 10%20% iridium platinum may be used. Othercorrosion-resistant metals or alloys having still higher melting points may be used.4

The thickness of the sheet metal from which the electrode 20 is stamped is of the order of .005 to .012 inch. Thinner metal can be used if it has the requisite strength for holding an accurate setting ofthe spark gap. l'I'he electrode 26 may have a total surface area of .1246 square inch, a sparking surface of .040 square inch, and a weight of 2.37 grains. These values are given by way of example only.

to become heated quickly by their contact with the gases. Toward the end of a power stroke the electrodes also' lose heat quickly as the temperature of the surrounding gases is reduced. The

changes in temperature of the electrodes closely follow those of the ambient atmosphere in which they operate. The rise in the temperature of the electrodes during the compression stroke so that they do not cool the gas at the spark gap is espe- `cially important in starting a cool or cold motor.

The electrodesr are actually heated by the heat of compression, during a compression stroke, to a temperature not materially lower than that of the compressed charge.

The grill 4or perforate construction of the electrodes of this invention makes it possible for the vllame ignited byl the spark to propagate into 'the main charge in the cylinder without having to travel between any extensive areas of closely spaced electrode surfaces.

A shell or ground electrode 26, shown in Figs. 4 4 0 and 5, is preferably a one-piece sheet metal stamping of the same material as the center electrode, and of a similar grill design and of like thinness. The total surface, sparking surface, and weight of the ground electrode 26 may be substantially equal to those of the center elec- 'trode 20. 'I'he ground electrode 26 has radial bars 21 connected by an upper or outer ring 26 and joined at their inner ends by a lower ring 29. The angular spacing of the bars 21 is the same as the angular spacing of the bars 2| of the center electrode 20, and the arcuate width of the bars 21 and 2| on the ground and center electrodes is preferably the same so that with the bars in registry the confronting faces of the bars provide sparking surfaces of substantially equal extent.

The

rings

28 and 23 of the ground electrode 26 are made of slightly larger diameter than theh The center electrode is welded to the spindle I0 in such relation to the threads on the core nut I3 that the outer face of the center electrode is at the desired spark-gap spacing from the ground electrode, and the bars on the

elecrings

22, 23 of the center electrode 26 in order to 60 provide a .short spark gap between the corresponding rings of the respective electrodes.

Both of the

electrodes

20 and 26 are of similar frusto-conical shapeup to and including the

rings

22 and 26, respectively. Beyond the ring 23 the ground electrode 26 has outwardly flaring legs or supports 30 that reach to the shell I6 and are preferably welded to the inside wall. lA shoulder 32 (Fig. 1) may be provided in the shell I6 for this connection with thel supports 36 of the ground electrode, or the supports may be buttwelded to the inner surface o f the shell bore. l

The spark gap between the electrode surfaces is preferably of the order of .005 inch or even less. The use of such a short spark gap is made trodes are in register when the core nut originally comes againstthe gasket I8 firmly. When adjustment of the spark gap eventually becomes necessary, such adjustment is effected by screwing down the core nut I3 further and compress ing the gasket I8. In this construction the adjustments are in steps since the core nut should be turned enough to bring the bars of the electrodes into registry at any new adjust ment with twelve bars as in the electrode grills shown in the drawings, the core nut would be turned through an angle of 30 or some multiple of 30, andthe pitch oi.' the threads on the core nut I3 determines the axial advance of the center electrode 26 with respect to theshell electrode 26.

Fig. 6 shows a spark-plug in which the spindle I0 has a long head and the mica insulation is set back in the plug where it is protected from the full heat of the cylinder. This construction makes a mica-insulated plug materially more resistant to exceptionally severe conditions.

When the plug is in use in an engine cylinder, gas is compressed in the space 36 (Fig. 1) within the plug. When pressure in the cylinder decreases after the peak pressure of the power stroke, gas flows from within the space 36 through the openings in the ground electrode 26, and this flow of expanding gas from the space 36 is a factor in the cooling of the electrode to prevent pre-ignition on the next compression stroke. The center electrode is similarly cooled, partly by the flow of gas from the space 36 and vby the center electrode.y

Figs. 'Z and 8 show a modied form of the invention in which corresponding parts are designatedfby the same reference character as in Fig. 1 but with a prime appended. The center electrode 20 differs` from the center electrode of Fig. 1 by the flatter angle of its frusto-conical sparking vsurfaces and the additional length of the supports 24'. The additional length of the supports 24 reduces the heat flow from the electrode20' into the metal of the spindle l0'. The heat flow can be still further reduced by omitting some of the supports 24'. In the various illustrated forms of the invention the legs or supports by which the electrodes are connected to the spindle or shell of the spark-plug are of small cross-section and of considerable length so that heat flow from the sparking surfaces by conduction through the metal is not great.

'I'he ground electrode 26 has its -sparking surfaces uniformly spaced from the complementary face of the center electrode 2li', and the supports 30' are extensions of thev lower part of the electrode 2S without change of angle. The supports 30' are welded to an outside shoulder instead 'of an inside shoulder as in Fig. 1.-

Figs. 9 and 10 show a modified form of the invention in which a center electrode Ill has a perforate frusto-conical outwardly extending flange 4l with angularly spaced, upwardly extending supports 62 welded to the lower end of a spindle 43. A ground electrode 65 is similar to Ithe ground electrode 26 of Fig. 7 except that its supports 51 extending to the .shell I6 of the spark-plug are only six` in number. 'I'his reduces the heat iiow to the shell. l

Other changes and modifications can be made, and some features of the invention can be used without others.

I claim:

1. In a spark-plug, an electrode comprising a sheet metal grill, and a second electrode with surface areas confronting the surfaces of the grill and spaced from said surfaces to make the spark gap of substantial lateral extent.

2. A spark-plug including two electrodes made of sheet metal and evenly spaced from one another over surface areas, the space between said areas being the spark gap.

3. A spark-plug including sheet metal electrodes of platinum alloy,- and having confronting complementary surfaces with the space between said faces providing the spark gap.

4. Ina spark-plug, two electrodes spaced from one another to make a spark gap and constructed of Zcorrosive-resistant sheet metal of extremely high melting point, said electrodes having confronting complementary surfaces with the space between said surfaces providing the spark gap.

5. A spark-plug, having a shell portion and a center spindle, a center electrode comprising one or more rings, outwardly extending bars angularly spaced around the axis of the spindle, and supports by which said electrode is connected to the spindle, and a ground electrode connected to the shell portion of the spark-plugand comprising one or more rings and radially extending bars at the same angular spacing as the bars of the center electrode and positioned in registry with the bars of the center electrode.

6. In a spark-plug, a center electrode and a ground electrode, each comprising a sheet metal grill and having a surface area opposing an area of the otherelectrode at a spacing of the order of .005 inch.

7. A spark-plug including an electrode which comprises outwardly extending bars converging toward their lower ends and connected at their lower ends by a ring, and a complementary electrode of frusto-conical shape with its surface at the same angle as the converging bars of the first electrode.,

8. In a spark-plug, confronting electrodes with" surface areas spaced to make the spark gap, the

' surface area on each side of the gap being the mass in relation to the surface area that is ,ex-

surface of a thin metal member of an order of thickness of .005 to .012 inch.

9. A spark-plug including sheet metal electrodes with spaced surface areas on opposite sides of and dening the spark gap, the thickness of said electrodes being of the order of .005 to .012 inch and the electrodes being made of material from the group containing 10%-20% rhodium platinum and 10%-20% iridium platinum.

10. A spark-plug electrode comprising a sheet metal grill with concentric rings connected by outwardly extending bars, and spaced supporting members extending from and beyond the outer rings of the grill for connecting the electrode with a supporting portion of a spark-plug.

, l1. In a spark-plug, a spindle, and a hollow electrode connected with the lower end ofthe spindle, said electrode having openings through which gases flow into and out of the interior of the electrode with changes in the pressure in an enginecylinder when the spark-plug is in-use.

12. In a spark-plug, a spindle of substantial mass and heat conductivity, a grill electrode of small mass and large surface area in proportion to its mass, said electrode including spaced connecting means of substantial length and limited cross-section connected with the spindle, and said electrode enclosing a space into and out of which gases flow when the spark-plug is exposed to the combustion space within a cylinder.

13. A spark-plug including twospaced elec,-

trodes of small mass in relation to their surface areas and both of which have their sparking surfaces spaced from the more massive portionsof the plug but supported from certain of said portions by thin .supports of the order of thickness of the electrodes to reduce heat ow from the sparking surfaces.

14. A spark-plug including two electrodes, each of which is of thin sheet metal to obtain a small posed to contact with surrounding gases, and

- each of which has supporting connections ofl re.

duced cross-section to retard heat ow from the electrode.

15. A low-voltage spark-plug including electrodes with surface areas having a spacing of the order of .005 inch, said electrodes being of such small. mass in relation to their surfaces that they are. quickly heated by compression of the gas charge in an engine cylinder. 'v

16. A spark-plug with electrodes of small mass in relation to confronting surface areas, said confronting areas of the respective electrodes being long and narrow, and equally spaced fromone another over` a substantial area to make the sparkgap. l 1

17. A spark-plug including in combination a shell, a spindle, a core nut by which the spindle shell and welded to said shell, the confronting l0 faces of the electrodes being at the desired spark gap spacing and their bars in registry when the core nut is initially screwed into firm contact with the gasket, and the electrodes being so positioned that their surfaces can be moved close: together, to compensate for wear, by screwing the core nut further into the shell against the resistance of the crushable gasket.

GEORGE M. PAULSON.