US2895069A - Spark plugs - Google Patents

Description

July 14, 1959 P; DAVIS SPARK PLUGS Filed Oct. 8, 195

INVENTOR Dar/5 United States Patent SPARK PLUGS Putnam Davis, Larchmont, N.Y., assignor to Jet Ignition $0., Inc., Larchmont, N.Y., a corporation of New ork Application October 8, 1954, Serial No. 461,061 8 Claims. (Cl. 313- 143) this constricted passage or ignition chamber and a head or insert disposed in the end of the constricted passage opening toward the associated cylinder having helical passages establishing communication between the ignition chamber and nearly axial jet passages of smaller cross-section opening into the associated cylinder.

In a spark plug of the above described character, the combustible mixture is propelled through the jet passages and helical passages of the head into the ignition chamber during the compression stroke and the helical passages cause swirling of the mixture in the ignition chamber. It can be theorized that when a spark is made to jump across the gap between the electrodes, the swirling action in the ignition chamber will serve to draw the spark from a central portion of the gap toward the edge portion thereof, thereby increasing the length of the spark and decreasing its amperage. The lengthening of the spark reduces its heating effect on the electrodes and the danger of pitting of the electrodes, and it also makes the ignition more effective, particularly during starting. The combustible mixture ignited in the ignition chamber expands and is thereby forcibly ejected through the helical and jet passages of the head into the cylinder to ignite the main charge in the latter. By reason of the reduced cross-section of the jet passages, the ignited mixture ejected into the cylinder is accelerated during its passage through the jet passages to enter the cylinder at high velocities, thereby improving the ignition of the main charge in the cylinder. Upon ignition of the main charge in the cylinder, the pressure in the cylinder becomes greater than the pressure within the body of the spark plug so that hot burnt gases start to re-enter the ignition chamber. However, such hot burnt gases are cooled by expansion in flowing from the jet passages of relatively small cross-section into the helical passages of larger cross-section. From the foregoing, it is apparent that heating of the electrodes from both the heat of the spark itself and the heat of the hot burnt gases which reenter the spark plug body is materially reduced thereby to increase the operative life of the electrodes and, hence, of the spark plug having the above described characteristics.

However, considerable difficulty has been experienced in manufacturing spark plugs having the above described characteristics, and the helical passages and restricted jet passages at the end of the spark plug body opening into the cylinder have been produced only at relatively great expense thereby decreasing the attractiveness of the-operative advantages achieved by such passages.

Accordingly, it is an object of the present invention to provide an improved construction for spark plugs of the described character whereby the cost and difiiculty of forming the helical passages between the ignition chamber of the spark plug and the communication with the cylinder and of constricting that communication are materially reduced.

A feature of this invention resides in the provision of a generally cylindrical head or insert defining the end of the ignition chamber within the spark plug body facing toward the cylinder and carrying one of the electrodes, the cylindrical head having several helical grooves in the surface thereof opening radially outward and at the opposite end faces of the head so that the helical passages are defined between said grooves and the adjacent inner wall surface of the spark plug body. In order 'to facilitate the machining of the helical groovesin the -'between a relatively large diameter portion of the interior of said body, in which the head is seated, and 30 the spark plug body opening into the cylinder.

a relatively small diameter portion of the interior'of In one embodiment of the invention, the outer surface of the head or insert, at the end of the latter facing toward the cylinder, is bevelled to seat against the inclined shoulder on the inner wall surface of the spark plug body, whereby the ends of the helical passages adjacent the small diameter portion of the interior of the body are constricted, while in another embodiment of the invention the inclined shoulder is disposed immediately adjacent the end of the head facing toward the cylinder so that the constriction is provided between the adjacent ends of the helical passages and the small diameter portion of the interior of the body opening into the cylinder.

The design will give a swirling action to jet flames coming out of the plug. Such swirling jets of flame increase the turbulence of the gas-air mixture in the cylinder of the engine and assure better mixture of the gas and air and more complete and rapid combustion.

As a result of the low pressure area in the vortex created by the swirling gas-air mixture entering the combustion chamber of the plug on the compression stroke there is less resistance (pressure) in the vortex, where the spark travels, than would be the case if the pressure were equal throughout the entire combustion chamber. There is therefore a lower compression ratio in the vortex than there is throughout the balance of the combustion chamber of the plug and cylinder of the engine.

The degree of taper and direction of taper of the holes or grooves make possible the control of the heat range of the plug other than by the conventional method now employed of increasing or decreasing the length of the nose of the ceramic to decrease or increase the rate of heat dissipation. i

The above, and other objects, features and advantages t of the invention will be apparent in the following detailed description of illustrative embodiments thereof which is to be read in connection with the accompanying drawing forming a part hereof, and wherein:

Fig. l is an elevational view of a spark plug embodying this invention, with the spark plug body being broken away and shown in section;

Fig. 2 is a transverse section taken along the line 2-2 of Fig. l, but on an enlarged scale;

Fig. 3 is a transverse section taken along the line 3-3 of Fig. l, but on an enlarged scale;

Fig; 4 is a perspective view of an element included in the spark plug of Figs. 1, 2 and 3;

Fig. 5 is a fragmentary elevational view of a spark plug constructed in accordance with another embodiment of this invention, and with the spark plug body broken away and shown in section;

Fig. 6 is a transverse section taken along the line 6-6 of Fig. 5;

Fig. 7 is a perspective view of an element included in the spark plug of Figs. 5 and 6; and

Fig. 8 is a fragmentary elevational view of another form of insert.

Referring to the drawing in detail, and initially to Fig. 1 thereof, the spark plug embodying this invention and generally identified by the reference numeral 10 is there shown to include an insulator 11, of conventional construction, and a hollow metal body 12. The body 12 defines an interior space or passage 13 which tapers toward the lower end of the body and communicates with a cylindrical space 14 forming an ignition chamber. The insulator 11 extends into the body 12 from above and is held in position by a jam nut 15, with a suitable seal, for example, a gasket 16 being provided between the insulator 11 and the side wall surface of the tapering space 13.

At its lower end, the insulator 11 carries a first electrode 17 disposed in the ignition chamber 14, and a second electrode 18 extends upwardly from an insert or head 19 toward the electrode 17 in axial alignment with the latter.

As is usual, the lower portion of body 12 is externally threaded, as at 20, for engagement in a suitably tapped hole or opening in the cylinder head (not shown).

In accordance with this invention, the body or insert 19 is substantially cylindrical and is formed with several helical grooves 21 in the side surface thereof and opening radially and at the opposite end faces of the insert 19. Each of the grooves 21 has a constant depth along the length thereof with respect to the axis of the insert 19 and has an arcuate cross-section of the same curvature along its entire length so that the machining of the grooves can be easily and inexpensively accomplished.

As seen in Fig. l, the cylindrical space or chamber 14 of the body 12, into which the insert 19 is pressed or otherwise secured, is bounded at its lower end by an inwardly inclined shoulder 22 which separates the space 14 from a passage 23 of relatively small diameter opening at the lower end of the spark plug body, and hence, into the cylinder.

In the embodiment of the invention illustrated in Figs. 1 to 4, inclusive, the side wall surface of the insert or head 19 is tapered or bevelled at the lower end, as at 24 (Figs. 1 and 4), and at the same angle as the inclined shoulder 22, so that the bevelled end 24 of the insert 19 in the space 14 seats upon the shoulder 22.

It is apparent that helical passages, communicating at their upper ends with the ignition chamber and at their lower ends with the passage 23 opening into the cylinder, are defined between the helical grooves 21 and the internal surface of the body 12 confronting the grooves. Sincethe upper portions of the grooves 21 are confronted by the cylindrical internal wall surface of the space 14, while the lower portions of the grooves are confronted by the inclined shoulder 22, it is apparent that the upper portions of the helical passages have relatively large cross-sectional areas (Fig. 3) and that the lower portions of the helical passages are constricted or have relatively small cross-sectional areas (Fig. 2), these varying crosssectional areas being achieved with helical grooves having the same cross-sectional curvature and depth with respect to the axis of the insert 19 along the lengths thereof for ease in machining.

The operation of the above described spark plug 10 is as follows:

During the compression stroke of the piston in the associated cylinder, the combustible mixture enters the spark plug body 12 through the passage 23 and then travels through the helical passages, defined between grooves 21 and the confronting internal wall surface of the body, into the ignition chamber 14. The helical passages impart a swirling motion to the combustible mixture entering the ignition chamber. On ignition, the voltage applied to electrode 17 causes a spark to jump across the center of the gap between the electrodes 17 and 18. In one aspect, it can be theorized that the swirling motion of the mixture in the ignition chamber serves to draw the spark away from the center of the gap to the edge portion of the latter, thereby increasing the length of the spark and correspondingly decreasing its amperage. The lengthening of the spark in the above manner tends to reduce the extent to which it heats the electrodes and the danger of pitting of the electrodes, and the lengthened spark also improves the effectiveness of the ignition, particularly during starting.

Following ignition of the mixture in chamber 14, the ignited mixture expands and is thereby forcibly ejected through the helical passages and the passage 23 into the cylinder to ignite the main charge in the latter. Since the helical passages are constricted at the lower portions of the grooves 21 by reason of the inclined shoulder 22, the ignited mixture ejected into the passage 23 is accelerated and enters the cylinder at a high velocity thereby to improve the ignition of the main charge.

When the main charge in the cylinder is ignited, the pressure in the cylinder becomes greater than that in the body of the spark plug so that hot burnt gases start to re-enter the spark plug body through the passage 23 and the helical passages extending from the latter to the chamber 14. However, since the helical passages have smaller crosssectional areas at their lower ends than along their upper portions, the hot burnt gases expand during their travel through the helical passages and are thereby cooled before entering the chamber 14 containing the electrodes. Thus, the heating of the electrodes by the hot burnt gases is held to a minimum.

In the embodiment of the invention illustrated in Figs. 5, 6 and 7, the several parts of the spark plug are identified by the same reference numerals employed in connection with the corresponding parts of the embodiment of Figs. 1 to 4, inclusive, but with the letter a annexed thereto. Thus, the spark plug 10a includes an insulator 11a extending into the ignition chamber 14a defined within the metal body 12a, and the axially aligned and spaced apart electrodes 17a and 18:: are respectively carried by the insulator 11a and an insert or head 1% disposed in the ignition chamber.

As in the first described embodiment, the insert 19a is formed with several helical grooves 21a in the side wall surface thereof opening radially and at the opposite end faces of the insert, the grooves 21a being at the same depth with respect to the axis of the insert and having the same cross-sectional curvatures along their entire lengths for each in machining. As distinguished from the insert 19, the insert 19a (Figs. 5 and 7) is cylindrical along its entire length, with the exception of the grooves 21a, so that the lower edge of the insert 19a is held above the inclined shoulder 22a. Accordingly, the helical passages defined between the grooves 21a and the internal wall surface of body 12a, which is cylindrical throughout the length of the insert 19a, are of the same cross-sectional -area along their entire lengths. However, the inclined shoulder 22a confronts or extends partly across the lower ends of the helical passages to provlde a constriction between the latter and the relatively small diameter passage 23a opening into the cylinder. Thus, following ignition of a combustible mixture in chamber 14a, the ignited mixture passes through the heheal passages and is accelerated upon discharge from the latter into passage 23a past the shoulder 22a, thereby to enter the cylinder at high velocity. Further, after ignition of the main change in the cylinder, any hot burnt gases re- .entering the body 12a are expanded and correspondingly cooled during passage by the shoulder 22a before entering the helical passages. From the foregoing, it is apparent that the spark plug a has the same operative advantages as the plug 10 although the constriction at the ends of the helical passages opening toward the cylinder is effected in a different manner.

Another form is illustrated in Fig. 8, wherein body 12 has insert 25 with tangentially drilled holes 26, the flames from said holes striking the interior of the body 12 or wall 27 to produce a swirling action. The holes 26 may be tapered in either direction.

Although specific illustrative embodiments of the invention have been described in detail herein and shown in the accompanying drawing, it is to be understood that the invention is not limited to these precise embodiments and that various changes and modifications may be effected therein without departing from the scope or spirit of the invention, as defined in the appended claims.

What is claimed is:

1. A spark plug comprising a hollow body having a cylindrical internal space defining an ignition chamber and a smaller diameter passage opening at the adjacent end of the body, with an annular inclined shoulder between said cylindrical internal space and smaller diameter passage, two axially aligned and spaced apart electrodes in said ignition chamber, and a substantially cylindrical insert in said cylindrical internal space at the end of the latter adjacent said passage, said insert having its lower external wall inclined inwardly so as to seat on said annular inclined shoulder, said insert having helical grooves in the side wall surface opening radially and at the opposite end faces of the insert so that helical passages are defined between said grooves and the internal wall surface of said body to communicate said ignition chamber with said small diameter passage while said inclined shoulder defines a constriction adjacent the ends of said helical passages opening towards said small diameter passage.

2. A spark plug comprising a hollow body having a cylindrical internal space defining an ignition chamber and a smaller diameter passage opening at the adjacent end of the body, with an annular inclined shoulder between said cylindrical internal space and smaller diameter passage, two axially aligned and spaced apart electrodes in said ignition chamber, and a substantially cylindrical insert in said cylindrical internal space at the end of the latter adjacent said passage, said insert having its lower external wall inclined inwardly so as to seat on said annular inclined shoulder, said insert having helical grooves in the side Wall surface opening radially and at the opposite end faces of the insert, said grooves being of the same depth with respect to the axis of said insert and having the same cross-sectional curvature along the lengths thereof, said grooves and the confronting internal wall surface of the body defining helical passages communicating said ignition chamber with said small diameter passage while said inclined shoulder defines a constriction adjacent the ends of said helical passages opening towards said small diameter passage.

3. A spark plug comprising a hollow body having a cylindrical internal space defining an ignition chamber and a smaller diameter passage opening at the adjacent end of the body, with an annular inclined shoulder between's'aid cylindrical internal space and smaller diameter passage, two axially aligned and spaced apart electrodes in said ignition chamber, and a substantially cylindrical insert in said cylindrical internal space at the end of the latter adjacent said passage, said insert having its lower external wall inclined inwardly so as to seat on said annular inclined shoulder, said insert having helical grooves in the side wall surface opening radially and at the opposite end faces of the insert, said grooves being of the same depth with respect to the axis of said insert and having the same cross-sectional curvature along the lengths thereof, the end of said insert facing toward said small diameter passage being bevelled and seating against said inclined shoulder so that helical passages are defined between said grooves and the confronting internal wall surface of said body with the cross-sectional areas of said helical passages at the ends opening into said ignition chamber being larger than the cross-sectional areas thereof at the ends opening into said small diameter passage.

4. A spark plug comprising a hollow body having a cylindrical internal space defining an ignition chamber and a smaller diameter passage opening at the adjacent end of the body, with an annular inclined shoulder between said cylindrical internal space and smaller diameter passage, two axially aligned and spaced apart electrodes in said ignition chamber, and a substantially cylindrical insert in said cylindrical internal space at the end of the latter adjacent said passage, said insert having its lower external wall inclined inwardly so as to seat on said annular inclined shoulder, said insert having helical grooves in the side wall surface opening radially and at the opposite end faces of the insert, said grooves having the same cross-sectional areas along the lengths thereof and the portions of said insert between said grooves having the same radius as said cylindrical internal space throughout the length of said insert, said insert being arranged in said cylindrical internal space with an end face of the insert contiguous with the large diameter end of said inclined shoulder, said grooves and the confronting internal wall surface of said body defining helical passages between said ignition chamber and said smaller diameter passage with said inclined shoulder forming a constriction adjacent the ends of said helical passages opening into said smaller diameter passage.

5. A spark plug comprising a hollow body having a stepped interior opening axially at the relatively small diameter portion thereof for communication with a cylinder and with an inclined shoulder between said relatively small diameter portion and the relatively large diameter portion of said stepped interior, an insulator extending into said large diameter portion of the interior through the end of the latter remote from said shoulder and carrying a first electrode, and an insert in said large diameter portion of the interior against said shoulder and carrying a second electrode axially aligned and spaced apart with respect to said first electrode, said insert having its lower external wall inclined inwardly so as to seat on said annular inclined shoulder, said insert having at least one helical groove in the periphery thereof opening radially outward and at the opposite end faces of the insert, each of said grooves and the confronting internal surface of said body defining a helical passage communicating the space around said electrodes with said small diameter portion of the interior while said inclined shoulder defines a constriction adjacent the end of said helical passage opening into said small diameter portion of the interior.

6. A spark plug according to claim 5; wherein each groove of the insert has the same depth with respect to the axis of the insert and the same cross-sectional curvature along its entire length.

7. A spark plug according to claim 6; wherein the end of said insert adjacent said small diameter portion of the interior has a bevelled edge seating face-to face against said inclined shoulder so that the portion of said has a smaller cross-sectional area than the remainder of said helical passage.

8. A spark plug according to claim 6; wherein said insert has the same cross-sectional configuration throughout its length and is Wholly contained in said large diameter portion of the interior so that said helical'passaige has the same cross-sectional area throughout its length and the constriction defined by said inclined shoulder isdisposed between said small diameter portion of the interior and the adjacent end of said helical passage.

References Cited in the file ofthis patent UNITED STATES PATENTS Spencer Apr. 4, 1911 Gottlieb Apr. 12, 1921 Gavlak Oct. 13, 1925 Powell Sept. 23, 1930 Harper Aug. 23, 1938 Harper June 18, 1940 FOREIGN PATENTS France Nov. 18, 1953

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