US2125035A - Electric ignition system and sparking plug for internal combustion engines - Google Patents

Description

- W. B. SMITS AND SPARKING PLUG FOR INTERNAL COMBUSTION ENGINES July 26, 1938.

ELECTRIC IGNITION SYSTEM Filed Oct. 19, 1936 INVENT R {;&e 8 e/ Ma /4754 Patented July 26, 1938' PATENT OFFICE ELECTRIC IGNITION SYSTEM AND SPARK- ING PLUG FOR INTERNAL COMBUSTION ENGINES Wytze Beye Smits, Kassel-Wilhelmshohe,

; Germany -Application October 19, 1936, Serial No. 106,431 In Germany October 18, 1935 10 Claims.

(Granted under the provisions 01' sec. 14, act of March 2, 192']; 357 O. G. 5)

This invention relates to ignition systems for internal combustion engines and has as a primary object the provision of a system utilizing a condenser charged with a current of relatively low tension and which is discharged directly across the electrodes of the sparking plugs.

A further object is to provide in a system of this character an ignition circuit arrangement including a condenser alternately charged and discharged directly across the electrodes of a sparking plug.

A further object is the provision of an ignition system for internal combustion engines by which the operating current employed may be of materially lower tension than is the tension of current conventionally employed in the firing of known types of sparking plugs as utilized in the art prior to the advent of this invention.

Other objects will be apparent from the description.

Developments of recent years have led to a constant increase in engine emciency combined with a saving in petrol. This goal has been attained by means of a constant increase of the pre-compression pressure, but a limit has been set on this development by the sparking plug. At a high compression pressure there results also a high temperature. At these high temperatures the internal surface leakage paths of the high tension insulators must be kept small, whereby on the other hand they are rendered very sensitive to oil.

The plugs must for a determined engine always be able to attain a certain self-cleaning temperature in order that the surface leakage paths of the high tension insulators can be burnt free from soot and other residues of combustion. This principle has made necessary the large number of types of sparking plugs which the plug manufacturers have to market at the present tin e. A new engine of one and the same manufacture requires various types of plugs in accordance with whether the engine is new or has been run in or whether it has already covered a relatively large distance. From this results the following law, based on experience: A plug with a high intensity of incandescence is extremely sensitive to oil. A plug which is very insensitive to oil has a correspondingly low intensity of incandescence. As a result of these two characteristics a limit is now set to the present development of high-compression engines, since the one characteristic excludes the other.

Turning briefly to the electric ignition itself, it may be said that an infinite number of tests have shown that the most favorable tension is one of 15,000 to 20,000 volts. It may be mentioned in this connection that in the change-over from magneto to battery ignition which has occurred in the course of the years the voltage itself has not been materially changed.

These relatively high tensions have been required in order at the considerable pressures which were necessary in the precompressed state in the cylinder to be able to bridge the electrode gap by a spark.

The employment of such a high tension in the region of 20,000 volts has, however, resulted in difficulties with the introduction of the insulated middle pole in a sparking plug, since it must be borne in mind also that the sparidng plug itself must be brought to fairly high temperatures in order that the insulation of the centre electrode may constantly burn free oi rust and carbon, in order thereby to maintain the maximum insula= tion of the centre pole. If these self oieaning temperatures are not reached, soot, carbon, gradually collects on the plug insulator, whereby a carbon connection between the centre pole and the external wall comes into existence, which then leads to the plug failing to spark.

The object or" the present application is an igni-= tion system which allows of these high voltages being materially dispensed with, whereby the insensitiveness of the plugs to being hindered in their working by oil or soot is very considerably increased.

The principal characteristic of the invention is the employment of a condenser which is charged with a current of relatively low tension and which is discharged directly across the electrodes of a sparking plug with a very narrow electrode gap.

This charging and discharging of the condenser is effected in any suitable manner and the current distribution to the sparking plug is controlled by suitable timing means such as, for example, a

commutator. This commutator assures the con trol of the ignition spark.

The advantage of an ignition system characterized as above described lies, above all, in a special energetic ignition of the inflammable mixture, whereby a better utilization of the fuel is guaranteed. Further, as has been indicated above, such a sparking plug actuated by condenser discharges is extremely insensitive to disturbance by oil, since also such a sparking plug with a condenser ignition always works perfectly, and must work perfectly in comparison to the high tension ignition employed hitherto, since with such a condenser ignition considerably lower tensions are employed.

Regarding the matter closely, it will be seen that carbon is the enemy of the present sparking plugs, while carbon particles with this new ignition system facilitate the discharge of the condenser and thus reliability is guaranteed under all possible working conditions.

The above described electric ignition system utilizes for ignition a quantity of low tension current which is stored up in a condenser.

An additional object of the present invention is an extension of the application of the system to engines running at high speeds. It is usual with such engines for use in racing cars and airplanes which are equipped with high tension ignition of approximately 30,000 volts to fit a double igniter in order to obtain perfect and powerful ignitions even at the highest rotation speeds. The avoidance in all circumstances of these costly double equipments when the invention is put into employment with low tension ignition of about 1,000 volts is an object of the present invention.

A further characteristic feature therefore resides in the fact that the above mentioned condenser as well as being discharged is also charged across the electrodes of the plug and thus in both cases produces a spark which institutes an ignition and respectively combustion. It results from this that the control mechanism requires to work at only one-half the number of revolutions which-apart from saving a costly double ignition installation-guarantees a considerably longer life and maximum certainty in working.

Figures 1 and 2 illustrate schematic arrangements of electric ignition systems for internal combustion engines as arranged in accordance with the invention.

Now the sparking plug systems employed for ignition at the present time are all founded upon the principle of high-tension ignition. With this it is necessary that the more central pole should be insulated from the other pole by a good heatresisting insulation with high insulating efficiency. The better this insulation is and remains, up to the electrode gaps, the more certain will such a sparking plug ignite.

In practical working there are many difficulties associated with these sparking plugs actuated by high tension. If we consider a sparking plug which has a high intensity of incandescence, we find that the projecting part of the insulation mass in the combustion chamber is very short; in the case of such a sparking plug with a small insulator and consequently short surface leakage path the vulnerability to disturbance by oil and soot is therefore very great. If, on the other hand, we consider a sparking plug offering good resistance to disturbance by soot and oil, we find that the insulation part which projects in the combustion chamber is very large. With this the surface leakage path is long and by reason of this the plug is less vulnerable to interference by oil and soot, but to balance this, the intensity of incandescence is lower. At the present day the limit of possibilities has been reached in this development. The present invention overcomes these difficulties (1) Because electric tensions of 20,000 volts are no longer employed, considerably lower tensions being used instead;

(2) Because these tensions are not led direct to the sparking plug; they are led indirectly over a condenser which discharges at the moment at which a charged condenser is connected to the sparking plug.

In order to obtain a proper transmission of this discharge to the sparking plug, the sparking plug must be so constructed that the distance between the electrodes is so small and the electrodes are so thick that the particles of oil, etc. which are deposited are not completely burnt off, for it is precisely these particles which form a means of assisting the condenser discharges. There exist two possibilities of successfully carrying through these procedures with a sparking plug.

(1) As described above;

(2) By making the insulation layer between the sparking plug poles so thin and the heat conduction from this place so great that the particles of oil and soot in question can easily deposit themselves on this layer and thereby greatly facilitate the condenser discharges.

By means of this manner of construction it is possible for the sparking plugs to have a high intensity of incandescence and at the same time to be extremely intensive to oil and soot, since it is precisely the particles of oil and carbon, and respectively the soot, which increase the operating efficiency of the sparking plug.

In the schematic Figs. 1 and 2, A designates the source of condenser charging current, B the changing switch, C is the condenser, D the sparking plug and E the ignition place.

Ignition systems are known in which a magneto charges a condenser which is subsequently discharged through the primary winding of an induction coil thus producing at each ignition a series of small sparks, that is to say, a high frequency spark. The present invention differentiates from such known systems by the fact that the condenser is charged and discharged directly across the electrodes of a spark plug producing thereby intense sparks and with the employment of only a relatively low voltage.

I claim:

1. Electric ignition system with direct discharging of a condenser across an ignition point, characterized in that the condenser is charged with a current having a voltage of the order of about 1,000 volts and is discharged across the electrodes of a sparking plug having a spark-gap width of the order of 0.3 mm. or less.

2. Electric ignition system according to claim 1, characterized in that the condenser is alternately charged and discharged across the electrodes of the sparking plug.

3. Electric ignition system according to claim 1, characterized in that the charging and discharging of the condenser is controlled by suitable timing means.

4. Electric ignition system with direct discharge of a condenser over a sparking distance characterized by that the condenser, free from every additional cooperating apparatus is charged by a low-tension current of about 1,000 volts or below and discharged over the electrodes of a spark plug, the air distance whereof is about 0.3 mm. or below so that combustion residues may be deposed there which favorize the condenser dis charge.

5. Electric ignition system according to claim 1, characterized in that the condenser is alternatively charged and then discharged over the very reduced insulation layer separating the ignition poles of a spark plug and whereupon combustion residues may be disposed.

6. Electric ignition system characterized in that it comprises a condenser exclusively charged by low-tension (about 1,000 volts or less) without any additional cooperating apparatus and at the discharge whereof only very short ignition distances (0.3 mm. or less) shall be bridged.

'7. In an electric spark plug ignition system composed of an ignition circuit and a condenser, the combination of only a low tension charged and discharged condenser of the order of about 1,000 volts with spark plug electrodes having a spark gap width of the order of less than 0.3 mm.

8. An ignition system for internal combustion engines, consisting of a spark plug, a condenser, a current source, and means for alternately charging and discharging the condenser from said current source directly across the spark plug terminals as the sole spark producing means therefor.

9. An ignition system for internal combustion engines, consisting of a spark plug terminal gap of less than 1 mm., a condenser, a current source of 1,000 volts or less, and means for alternately charging and discharging the condenser from said current source directly across the spark plug terminals as the sole spark producing means therefor.

10. An ignition system for internal combustion engines, comprising in combination, a low voltage current circuit, a condenser receiving a charge therefrom, a spark plug, and means for discharging the condenser directly across the plug terminals as the sole spark producing means therefor. 7

WYTZE BEYE SMITS.

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