US2745980A

US2745980A - Surface discharge plug for low tension and condenser discharge

Info

Publication number: US2745980A
Application number: US274607A
Authority: US
Inventors: Smits Wytze Beye
Original assignee: Smitsvonk N V Res Lab Comp
Current assignee: Smitsvonk N V Res Lab Comp; Smitsvonk N V Research Laboratory Comp
Priority date: 1952-03-03
Filing date: 1952-03-03
Publication date: 1956-05-15
Anticipated expiration: 1973-05-15

Description

May 15, 1956 w. B. SMITS 2,745,980

SURFACE DISCHARGE PLUG FOR LOW TENSION AND CONDENSER DISCHARGE Filed March 3, 1952 INVENTOR M725 5292 .snwzs,

BY QLEAERQ ATTORNEYS United States Patent SURFACE DISCHARGE PLUG FOR LOW TENSIGN AND CONDENSER DISCHARGE Wytze Beye Smits, Voorburg, Netherlands, assignor to Smitsvonk N. V. Research Laboratory Comp., Rijswijk, Netherlands Application March 3, 1952, Serial No. 274,607

1 Claim. (Cl. 313-431) The invention relates to a surface discharge spark plug for low tension and condenser discharge. Spark plugs of this type are known, for example from the Netherlands patent specifications Nos. 46,114, 55,918 and 62,644. Further, such spark plugs have been described in an article by W. Bye Smits in the periodical De Ingenieur, 63, No. 3, p. V. 1/9 (January 19, 1951), entitled: The Smitsvonk Low Tension Capacity Ignition.

Such spark plugs normally have a flat operative surface, which comes to lie approximately on a level with the wall of the combustion space.

It has been found that in some cases these known spark plugs do not operate quite satisfactorily, more in particular not in poorly scavenged two-stroke engines. Especially many small two-stroke engines are insufl'iciently scavenged, for example because the crank-case with the bottom of the piston is used as scavenge pump.

Now it has appeared from experiments that a better ignition can be attained in such cases when according to the invention one or more chambers are formed in the spark plug, in the side wall of which are located the operative parts of the electrodes, near the mouth of the chamber or chambers.

It is not certain to what cause this favourable effect is to be attributed. It is, however, probable, that in poorly scavenged engines a layer of combustion gases adheres to the walls of the combustion chamber, thus remaining in the neighbourhood of the spark plug. This layer will naturally expand and be compressed again upon expansion and compression respectively in the cylinder, but the layer will remain substantially present. The surface discharge sparks for the ignition will now therefore operate, at least partially, in gases which are combustion gases and which do not contain suflicient amounts of still combustible particles and air to start the combustion of the mixture efiiciently and rapidly. The consequence of this is misfiring and irregular operation of the engine. When one or more chambers, are provided according to the invention, the layer of combustion gas in the neighbourhood of the spark plug is probably forced, at least partially, into the chamber or chambers during the compression stroke. A quantity of foul gas thus accumulates in the deepest part of the chamber or chambers, as a result of which the layer of combustion gas present near the operative parts of the spark plug will disappear altogether or at least be greatly reduced in thickness. It is therefore essential that the operative parts of the electrodes are near the mouth of the chamher or chambers, since otherwise they would operate in the foul gas. This is in agreement with what was observed during experiments. It is, however, also possible that during the scavenging of the cylinder the chamber or chambers, owing to the interruption of the smooth surface of the combustion space, cause a vortex in this place when the scavenging-air current passes by, said vortex sufliciently rarefying any foul gases in the neighbourhood of the operative parts of the electrodes, and said vortex being maintained during the compression stroke, so that the combustion is started and propagated in a particularly fool-proof manner.

Although applicant suspects that the first-mentioned effect is the most likely explanation of the advantage obtained, it is not to be considered impossible that the two actions occur simultaneously and make their joint favourable influence felt.

The invention will now be explained more in detail with reference to two embodiments shown in the drawing.

Fig. 1 illustrates a spark plug according to the invention with a single chamber, in which the operative parts of the electrodes are provided in the side wall of the chamber, one part of the figure being a front View and the other part an axial cross-section.

Fig. 2 illustrates an embodiment in which the opera tive parts of the electrodes are provided in the top surface of the spark plug, in the side wall of the single chamber. This Fig. 2 only shows a part of a spark plug.

As shown in Fig. l, a spark plug according to the invention as usual, has a casing 1, connected to the ground, and insulating body 2, and a connecting terminal 3. The casing 1 has a screw-threaded section 4, by means of which the spark plug can be screwed, for example, into a cylinder cover or the like, electric contact with the ground being established via the screw-thread.

As shown in cross-section in Figs. 1 and 2, two electrodes 5 and 6 are located inside the screw-threaded section 4 of the casing 1, the said screw-threaded section 4 forming the connection with the electrode 6. The space between the electrodes 5 and 6 is filled up entirely or partially with a separator body 7 of only slightly conductive or semi-conductive material. In both spark plugs a chamber 8 has been provided, which is located coaxially in the spark plug and is cylindrical. This chamber has a depth which is greater than the diameter of the cylinder.

In the embodiment according to Fig. 1, in which the operative edges of the electrodes 5 and 6 lie in a circle along the side wall of the chamber 7, these edges are at a distance from the mouth of the chamber which is less than one third of the depth of the chamber.

In the embodiment according to Fig. 2, in which the operative edges of the electrodes are located in the top surface of the spark plug in the side wall of the chamber, these operative edges preferably lie in a concentric circle round the chamber 7. In a spark plug according to Fig. 2 the action will probably not be inferior to that in the embodiment according to Fig. 1, but a spark plug according to Fig. l is easier to make.

The invention may be embodied in several other ways as well. A number of chambers may be provided, each of these, for example, having operative parts lying concentrically around them. A number of chambers may also possess jointly a set of operative edges of electrodes.

Apart from the top surface, the chambers might also be provided in a side surface of the spark plug. Thus a construction is formed such as shown, for example, in Fig. 7 of the above-mentioned article in De Ingenieur, with the difierence that the operative edges of the electrodes are provided near the mouth instead of in the deepest part of the chamber.

I claim:

'Surface discharge spark plug arrangement for low tension and condenser discharge, comprising: means forming a chamber having its opening at the sparking end of said plug, said chamber consisting of a vaulted bottom and, extending from said bottom to said opening, unobstructed parallel sidewalls; sparking electrodes disposed intsaidt sidewalls forming. alpart thereof, said elec:

trodes. lying at a. distance, less than. one-.third the, depth. of the chamber from the. chamberopening, and; insulating material formingaspa'rkingsuriace disposed between said electrodes.

References Cited UNITED STATES PATENTS in the file of this patent Stephenson June 20, Brewster Mar. 6, Burhans Sept. 23, Mitchel Sept. 15, King Nov. 18, Mitchel Aug. 15,