US1221906A

US1221906A - Spark-plug.

Info

Publication number: US1221906A
Application number: US84900414A
Authority: US
Inventors: Max Rall
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1914-07-03
Filing date: 1914-07-03
Publication date: 1917-04-10
Anticipated expiration: 1934-04-10

Description

M. BALL.

SPARK PLUG. APPLICATION FILED JULY 3. m4.

Patented Apr. 10, 1917.

M/mJESSES 7L L M Ia/M UNITED STATES gram OFFICE.

MAX BALL, 0F PARIS, FRANCE, ASSIGNOR TO THE FIRM 0]? ROBERT BOSCH, OF

1 STUTTGART, GERMANY.

SPARK-PLUG.

Specification of Letters Patent.

Patented Apr. 10, 1917.

Application filed July 3, 1914, Serial No. 849,004.

trodes of spark plugs in electrical ignition systems for internal combustion engines is generally such as to raise those parts to the temperature of incandescence, and hereto fore in engines operating at high speed or under high compression, the temperature of the sparking electrode continued to be sufficiently-high during the succeeding compression stroke in the same cylinder to ignite the compressed combustible mixture and thereby cause premature ignition, which sometimes resulted in back-fire and stalling of the engine,.or at least in a considerable reduction of power output. In the usual type of spark plugs having an insulating sleeve of porcelain and also having an electrode rod extending therethrough and terminating in a sparking part, premature ignition has been due to the fact that the material and the dimensions of the electrode rod and the area of the surface exposed to the outside did not provide a rate bf heat conduction sufficiently high to cool the sparking part from the temperature of incandescence to a temperature below the point of ignition of the compressed combustible mixture in the short interval of time occurring between the explosion and the succeeding compression in the cylinder, especially when the heat developed in the cylinder during the working and compression strokes was considerable or when the explosions rapidly followed one another as at high speed.

An object of this invention is to provide a spark plug wherein the heat developed in the sparking part of the electrode is conducted away therefrom with sufficient rapidity to reduce theetemperature below the point of ignition of the compressed combustible mixture in the required interval of time, thereby precluding the possibility of a subject premature ignition; and another object is to provide means in this kind of spark plug for maintaining the sparking electrode fixed in longitudinal position relatively to the insulating sleeve and centered therein to thereby preserve the length of the spark gap, notwithstanding the expansion of the parts of the spark plug, the vibration and jar in operation and the slight inaccuracies in centering the electrode in the sleeve. In accordance with my invention, the central electrode comprises a sparking part of non-oxidizable metal capable of withstanding the ignition of the burning gases, and a support therefor of metal of high thermal conductivity extending through the insulating sleeve. Preferably, this support is made of copper or other suitable metal with a high coefficient of thermal conductivity, and is joined to the sparking part; or the sparking part is made integral with a central core which is enveloped in a sleeve or coating of copper or like metal throughout its length in the insulating sleeve. In order that the cross section of the support may be small, I

prefer to provide a radiation member exposing a comparatively large surface to the outside and being in close contact with the support so as to aid in the rapid conduction ofheat from the sparking part. Furthermore, I prefer to srovide a compensating device for maintaimng the sparking part of the electrode in fixed longitudinal position relatively to the insulating sleeve, notwithstanding the difference in expansion resulting from temperature changes in the two; and also to provide means for holding the sparking electrode centered in the insulating sleeve in order to maintain the length of the spark gap constant notwithstanding mechanical inaccuracies.

In the accompanying drawings, illustrating my invention,

Figure 1 represents a central section, partly in elevation, of the preferred form of spark plug;

Fig. 2 represents a modification of the sparking electrode thereof;

Fig. 3 represents a side elevation of the fastening ring for maintaining the angular relation between the sparking electrode and the insulating sleeve;

Fig. 4 represents a section on line 4-4 of Fig. 1;

. washer 9' Fig. 5 represents a top View of the insulating sleeve; and

Fig. 6 represents a side view, partly broken away, of the insulating sleeve.

The spark plug of Fig. 1 has an outer shell n of metal adapted to be screwed in a threaded opening in the engine cylinder, and a porcelain sleeve m securely clamped in the shell, as is Well known. The sparking electrode comprises a sparking parta having one or more sparking points as desired, and a support 5 extending centrally through the insulating sleeve m, the two being fastened together in any suitable way, as by turning the cupped part c of the sparking part over an enlargement Z on the end of the support therefor. The radiation member has a large area of exposed surface made up in any suitable Way, as by a series of washers c and 0' of alternately large and small diameter, and it is fitted tightly around the projecting end of the electrode support. The clampingnut d is screwed down on the threaded end of the electrode support against the compensating spring 7, and is locked in position by the locking nut 0?.

lit usually happens in practice that the insulating sleeve m is not exactly centered in the shell 12, and under this condition, the length of the spark gap, between the end of the sparking part a and the cooperative electrode formed by the shell n, changes as the sparking electrode is turned in the sleeve as a result of vibration of the engine. In the spark plug shown in Fig. 1, a change in the adjusted length of the spark gap from this cause is prevented by means of the having a diametrically disposed ridge 9 fitted in a complementary groove m" in the top of the insulating sleeve m to hold it fixed in angular position relatively to the sleeve,

end of the electrode support which has a. flat side at i, to hold it fixed in angular position relatively to the electrode support. In addition to these means for preventing alteration of the spark gap, I prefer to provide an asbestos cord tightly fitted between a re duced section, of the electrode support and the wall of the insulating sleeve, to thereby center the electrode support in the sleeve and prevent vibration of the sparking electrode relatively to the sleeve.

The speaking part of the electrode is exposed to the burning gases within the cylinder,and hence is made of nickel or other metal which resists oxidation and corrosion under these conditions, but which hav a comparatively low coeflicient of thermal conductivity. The support I) of the electrode is sealed to the cylinder by the cupped part c and by the insulating sleeve m, and since it is not subjected to the action of the burning gases, it does not have to resist oxiand also having aicentral open-, 'ing with a flat side at g? fitted around the naeneoe datio-n and corrosion, and is made of metal .having a high coefficient of thermal conducof copper whose cocopper or other metal of high thermal conductivity.

lnasmuch as the temperature coefficient of expansion of copper or other metal suitable for the electrode support 6 is quite different from that of porcelain, ofwhich the insulating sleeve m is made, I prefer to provide a compensating arrangement acting between the insulating sleeve and the sparking electrode to prevent 'longitudinal movement of the electrode in the sleeve, which would alter the length of the spark gap in case that the insulating sleeve was not exactly centered in the shell'n. The spring 7 and the nuts cl, 0! effect this result by maintaining the inner end of the sparking part a against the end of the insulating sleeve m, irrespective of the changes in length of the parts due to the temperature rise. Furthermore, the compensating arrangement holdsthe base portion of the sparking part. a in contact with the end of the insulating sleeve m and over the central bore therein, thereby preventing the burning gas in the cylinder from entering thebore and support 6.

Having thus described my invention, what I claim is:

1. In a spark plug, an insulating sleeve, and a sparking electrode comprising a sparking part of non-oxidizable metal and a support therefor extending through the sleeve and engaging said sparking'part, said support embodying metal having a coeficient of thermal conductivity considerably higher than that of the sparkingpart, and also having a cross section throughout its length considerably greater than the average cross section of the sparking part.

2. In a spark plug, an insulating sleeve, and a sparking electrode comprising a sparking part of non-oxidizable metal and a support therefor extending through the sleeve and engaging said sparking part, said support embodying metal having a coeficient of thermal conductivity considerably higher than that of the sparking part, and also hav-, ing a cross section throughout its length considerably greater than the average cross se tion of the sparking part, the sparking part beingsubstantially of conical, form with its base engaging .the support.

3. In a spark plug, an insulating-sleeve, and a sparking electrode comprising a sparking part of non-oxidizable metal and a copper support therefor extending through attacking the metal of the is about 77.6 compared with about I the sleeve and engaging said sparking part, the support having a cross section throughout its length considerably greater than the average cross section of the sparking part.

4. In a spark plug, an insulating sleeve, a sparking electrode comprising a sparking part of non oxidizable metal and a support therefor extending through the sleeve and embodying metal having a coefficient of thermal conductivity considerably higher than that of the sparking part, and a radiation member in contact with the support and having a large exposed surface for dissipating the heat therefrom.

5. In a spark plug, an insulating sleeve, 3. sparking electrode extending through the sleeve and terminating in a sparking part,

and a radiation member mounted on the other end of the electrode in contact there with and comprising a plurality of disks having alternately larger and smaller diameters and being made of metal of a high 00- efiicient of thermal conductivity.

6. In a spark plug, an insulating sleeve having a groove in its top surface, a sparking electrode extending through the sleeve and terminating in a sparking part, a washer surrounding said electrode and held against rotation with respect thereto, said washer having a ridge engaging said groove to hold the electrode in centered position in the sleeve, and means for maintaining the washer in said position.

7. In a sparkplug, an insulating sleeve, a sparking electrode extending loosely through the sleeve and terminating in a sparking part, locking means engaging the sleeve and the electrode to hold the electrode in centered position in the sleeve, and'means for preventing vibration of the electrode in the sleeve.

8. In a spark plug, an insulating sleeve, a sparking electrode extending loosely through the sleeve and terminating in a sparking part, locking means engaging the sleeve and the electrode to hold the electrode in centered position in the sleeve, and means surrounding the electrode and positioned within the sleeve for preventing vibration of the electrode in the sleeve.

In testimony whereof I aflix my signature, in presence of two witnesses.

' MAX BALL. Witnesses:

Eve Sunni,

E. BoDEL.