US 2093848 A
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p 1937. D. w. RANDOLPHETAL 2,093,848
METHOD AND APPARATUS FOR PRODUCING IGNITION Original Filed May 22, 1933 Elam Patented Sept. 21, I937 METHOD AND mm'rus roa rao ucme rom'rron Donald W. Randolph, Flint, and Ora 8. Dimendack and Ralph A. Wolfe, and Lewis B. Headrick,
Ann Arbor, Mlola, Harrison, N. J.
Application May 22, 1933, Serial No. 672,186 Renewed March 5, 1937 10 Claims.
'Ihis invention relates to methods and apparatus for producing ignition of the combustible charge in internal combustion engines and the like.
5 By our improved method the charge is ignited by electric discharge preferably at high frequency but instead of providing for discharge across the gap between a pair of electrodes separated by the gases in the combustion chamber as is now cusl tomary we arranged for discharge by the breaking down of a portion of a dielectric separating two plates of a condenser. The plates of the condenser are constituted by electrodes arranged in the ignition circuit. The dielectric may consist l of a solid and a gas arranged in series between the electrodes. The solid portion of the dielectric may be of heat-resisting insulating material, such as porcelain, mica or quartz, exposed in the combustion chamber and insulating one. of the electrodes. The gaseous portion of the dielectric is constituted by the combustion chamber gases extending between the solid dielectric and the other electrode. Upon application of high frequency voltage to the ignition device the gas- ;5 eous dielectric breaks down and electric discharge takes place between the surface of the solid dielectric and the adjacent electrode through the combustible gases in the combustion chamber, igniting the charge. 1
We have stated in a generic way the distinguishing features of our ignition system to emphasize its novel character and make clear to the reader the broad scope of the invention and the 5 many forms of devices in which it may be embodied. In the preferred form of our invention the ignition device takes the shape of a conven-'- tional spark plug, the center wire constituting one plate of the condenser, the usual insulator and the layer of gases surrounding the insulator constituting the dielectric and the metallic shell of the plug constituting the other plate of the condenser. The plug differs from conventional plugs in that the center wire is not exposed in the 5 combustion chamber, but stops short of the end of the plug and is entirely covered over by the material of the insulator. The insulation is made of reduced thickness adjacent the end of the plug where it is desired that the discharge take place, and preferably also the width of the air gap at this point is reduced as compared'with the gap at other points along the plug so that the electrical field is strongest at the discharge end of the plug. All of this has the effect of facilitating the passage of the discharge at the end of the plug where it is desired.
The invention has many advantages. One of the chief dimculties with present day plugs is that the electrodes are attacked by the combustion chamber gases, including the sulphur dioxide gas formed during the combustion of-fuei in which sulphur occurs as an impurity. With the electrode covered over by insulating material, it remains as good as ever throughout the life of the p ug.
Another difllculty with present day plugs is that the insulators become coated with carbon and other products of fuel combustion with the result that a path of low resistance is formed in parallel with the spark gap which short circuits the gap, rendering the plug inoperative. With the insulator properly designed and with the center wire sealed within the insulator, and nothing but the smooth surface of the insulator exposed in the combustion chamber there is little opportunity for the collection of carbon on the insulator. We have also found that a carbon coating is less effective in reducing or preventing high frequency discharge.
Another difficulty in present day plugs arises from the fact that the center wire being a good heat conductor, and directly exposed to the com- ,bustion chamber temperatures, it absorbs a great deal of heat which is directly transferred to the insulator thus increasing the insulator temperature more rapidly to a temperature sumciently high to cause preignition. With the center electrode sealed within the insulator, the electrode serves to cool the insulator rather than to heat it and the insulator is less liable to attain undesirably high temperatures.
In Figure 1 we have shown diagrammatically one .circuit in which our invention may be embodied. I In Figures 2 to 4 we have illustrated different designs of plugs made in accordance with our invention.
Figure 5 indicates a slightly modified circuit which may be used.
In Figure -1 there is illustrated a circuit which may be used in adaptingthe conventional spark coil ignition system of present day automobiles to our invention. At 4 we have indicated the usual six volt battery, at 6 the spark coil, having a primary 8 and a secondary It. At I! we have shown the usual circuit breaker which may be driven by the engine in the usual manner, and at it is shown the usual condenser bridging the breaker points to reduce sparking. In one design of apparatus that we successfully employed the ratio of secondary turns to primary turns in the spark coil was but to 1, whereas in present day low frequency installations the ratio varies from 34 to 1 to 79 to 1. This, of course, is a matter of design, the ratio of transformation varying with the installation.
Across the secondary It are arranged a condenser I6, and, in parallel with a condenser, a spark gap II in series with the primary 2! of transformer T. This transformer may take the form of the well known Tesla coil and may have simply an air core. The ratio of transformation employed in the specific design of apparatusreferred to above was 1 to 30. This may likewise be varied for diflerent installations. The condenser l6, gap l8, and primary coil 20 constitute a tuned oscillatory circuit. The oscillatory circuit may be tuned in any well known way as. by adjusting the length of the gap, the capacitance or inductance of the circuit. 22 indicates the secondary coil of transformer T, and in series with this coil is the distributor 23 which is provided with rotary arm 24 and a series of terminals 25, each provided with a lead 21 to one of the ignition devices 26. The distributor is driven from the-engine inthe usual manner, and may be of conventional design.
The ignition device 26 may be in the form of a spark plug as shown in Fig. 2. 28 indicates the usual shell adapted to be threaded in an opening in a wall of the combustion chamber, and here shown as provided with the usual side electrode 30 at its lower end. The center electrode 32 extends to within a short distance of the end of the insulator 33, and at its upper end is provided with a suitable terminal 34 for connection with the lead 21 from the distributor 23. It will be noted that the insulator 33 is of minimum thickness at its lower end, providing minimum dielectric strength to confine the discharge to this part-of the plug.
The shell 28 is grounded in the engine block in the usual manner, and for simplicity in wiring the primary and secondary of the spark coil 6, the condenser l6 and the primary and secondary of the transformer T are provided with a common ground connection as shown at G.
The ignition system operates as follows: With the distributor in position to send an impulse to a spark plug as shown in Figure 1, the
circuit of the primary 8 of the spark coil 6 is ciently great to cause a spark to jump across the gap at i8. The tuned circuit constituted by condenser i6, gap l8, and primary 20 of transformer T is then set oscillating. The oscillating circuit is designed for frequencies of the order of 1,000,000 cycles per second. If desired, however, 3,000,000 cycles or even more may be employed, and there is also considerable latitude permissible under 1,000,000 cycles.
The oscillating high frequency current in the primary 20 of transformer T induces a high frequency electromotive force in the secondary 22, which causes a high frequency current in the circuit consisting of the secondary 22, the distributor 23 and the plug 26 selected by the distributor 23. The center electrode 32 of the plug constitutes one plate of a condenser and the side electrode 30 the other plate. The dielectric consists of the adjacent portion of the insulator 33 and the gap which separates the insulator from the side electrode. Upon application of the high frequency voltage the gases filling the gap are broken down and electric discharge takes place between the electrode 30 and the adjacent surface of the insulator. This discharge is not confined to the very tip of the insulator but takes place over quite a wide area at the end of the plug.
. the electrode.
threaded within the insulator.
chamber will show that not only do sparks pass to the electrode, and occasionally to other points on the shell, but the spark discharge is also accompanied by a blue glow in the adjacent gases which will in itself initiate combustion.
The same action takes place as the distributor armmoves to positions to send impulses in rotation to the other plugs. If desired, the side..electrode 30 may be dispensed with entirely, with equally good results for in this case discharge takes place in the form of a glow and a spray of large and small sparks going from the center electrode to the side of the shell.
Our ignition system thus consists essentially of a source of electrical oscillations of high frequency impressing impulses upon a circuit which includes the ignition device, and is coupled to the oscillating circuit in any desired manner. We have illustrated electromagnetic coupling, but obviously electrostatic or resistance coupling may be substituted if desired. In the case of electrostatic or resistance coupling it would be necessary to use a higher ratio of transformation in the spark coil since the type of coupling does not permit stepping up the voltages. The difiiculty in designing an efiicient spark coil of suitable ratio of transformation renders these methods of coupling impractical at the present time. The circuit consisting of the coil 22, distributor 23, conductor 21, and igniting device 26, and completed by ground connection, we have termed the igniting circuit. Obviously to secure the maximum efiiciency in the transmission of electrical energy the circuit should be tuned so that it is in resonance.
In Figure l we have illustrated a form of damped oscillatory circuit including a spark gap. Obviously, if desired, a source of undamped oscillations might be used, such as the ordinary vacuum tube, but owing to the fact that to secure the desired power it would be necessary to use a power tube of large size, the expense of this method would probably be prohibitive.
In Figure 3 we have illustrated an ignition device differing slightly from that shown in Figure 2. As in that figure, the insulator 33' is preferably made of porcelain, fused quartz, or other material having suitable insulating and heat resisting properties but in this form the end of the insulator is flattened asat 36 and is flush with the lower end of the shell 28'.
In Figure 4 is shown a further modification in which a fused quartz insulator 33" is used. As in the other forms the center electrode 32" stops short of the lower end of the insulator so that it is completely shielded from the effects of the combustion gases.
In a conventional spark plug it is essential to seal the center electrode in the insulator to prevent the leakage of combustion chamber gases,
from the combustion chamber between the center electrode and its bore. In the ignition devices shown it is obviously not necessary to do this since the combustion chamber gases cannot reach The electrode may be Simply Thus by our improved construction the sealing problem is entirely avoided.
If desired we may dispense with the side electrode altogether and in this case the sparks and glow pass from the tip of the insulator to various points around the shell, as previously described.
We have illustrated in Figure an alternative form of circuit which we may employ if desired. The chief difference consists in the fact that the distributor 23' is arranged in the oscillating circuit containing the primary of the Tesla transformer T. With this design instead of employing one transformer or Tesla coil for all the ignition devices, it is necessary to provide one for each cylinder. These may be conveniently made in the form of attachments to the individual spark plugs.
' Referring to Figure 5, 4 is the battery, I2 the circuit breaker, mechanically operated as before, and bridged by the usual condenser ll 6 is the usual spark coil having a primary 8 and a secondary i0. i8 is the spark gap across the secondary of the spark coil. In parallel with the spark gap is arranged, in series, a condenser IS,
the distributor 23, and the primary of the transformer or Tesla coil T. The secondary III of the spark coil, the corresponding side of the spark gap l8, and the primary 20 of the transformer T are grounded as shown at G. The ignition device 26 which may be of any of the described constructions, completes the secondary circuit of the transformer. While not illustrated, it is to be understood that each point on the distributor is connected to a transformer T' in the same manner as the one illustrated.
The above circuit operates the same as that first described. The chief advantage resides in the fact that there is less chance for leakage of electrical energy.
Obviously the sparking device may take many other forms. Functionally it is a condenser in which electrical discharge takes place through the gaseous portions of the dielectric.
We have referred to the fact that a blue glow occurs at the same time as the spark discharge. We are not in a position to say definitely what part of the phenomena produces ignition or even is the greatest factor in producing it. Whatever be the exact nature of the phenomena, we have succeeded in successfully running internal combustion engines with our improved system with the advantages described above, and that invention is specifically pointed out in the appended claims.
1. Means for igniting a combustible mixture comprising an electrical circuit, a condenser in the circuit exposed in the combustion chamber and including a solid and a gaseous dielectric in series, the gaseous dielectric being constituted by the gases in the chamber, and means for supplying the circuit with electrical energy to produce electrical discharge through the gaseous dielectric, the dielectric strength oi the solid dielectric being sufiicient to prevent discharge therethrough.
2: In the combination as defined in claim 1. said last named means comprising a source of ---high frequency electrical oscillations.
3. Means for igniting a combustible mixture comprising an oscillating circuit, means for setting up high frequency oscillations in said circuit, and an igniting circuit coupled to said oscillating circuit and comprising va condenser exposed to the combustible mixture and comprising a dielectric, part of which is constituted by the mixture and is subject to electrical discharge as a result of the said oscillation.
4. Ignition apparatus comprising a tuned oscillatory circuit, means for setting up high frequency oscillations in said circuit, and an ignition circuit coupled to said tuned circuit and including a distributor and a. condenser in series, said condenser being arranged for exposure in the combustion chamber and being of sufficient dielectric strength to prevent puncturing by the spark.
5. An ignition device comprising an insulator arranged to be exposed in the combustion chamber, a conductor embedded in the insulator and having its lower end covered thereby, and a conductor adjacent the lower end of the insulator and in series with the first named conductor to form a condenser with the adjacent portion of the em bedded conductor, said insulator being of sumcient dielectric strength to prevent puncturing by the spark passing between said conductors.
6. An igniting device comprising a shell, an insulator in the shell, an electrode in the insulator having its lower end covered thereby and protected from combustion gases, said insulator being of suflicient dielectric strength to prevent puncturing by the spark passing between the shell and the electrode.
7. An igniting device comprising a shell, an insulator in the shell, an electrode in the insulator having its lower end covered thereby, the thickness of insulation separating the electrode and the shell being a minimum adjacent the lower end of the insulator, said insulator being of sufficient dielectric strength to prevent puncturing by the spark passing between the shell and the electrode.
8. An igniting device comprising an insulator,
an electrode embedded in the insulator with one end exposed and the other end sealed within the insulator and protected from combustion gases, and a conductor adapted for positioning in the combustion chamber adjacent the sealed end of the insulator, the insulator being of minimum thickness between the electrode and conductor to insure discharge at that point, said insulator being of sufiicient dielectric strength to prevent puncturing by the sparks passing between the electrode and conductor. h
9. An ignition device comprising a condenser having conductors separated by a solid dielectric and a gaseous dielectric in series, and adapted'for positioning in the combustion chamber, the solid dielectric being of sufficient strength to prevent puncturing upon application of sparking voltage. 10. An ignitionsystem comprising, in series, a source of electrical energy, an interrupter, and the primary of a transformer, a circuit coupled to the first named circuit and comprising the secondary of the transformer, and, in parallel with the secondary, a condenser and the primary of a second transformer, a spark gap in series with both of said last named devices, said three last named devices constituting a high frequency oscillating circuit, and an igniting circuit comprising the secondary of the second transformer, 'a plurality of igniting devices in the form of condensers adapted for positioning in the combustion chambers and being of sumcient dielectric strength to prevent puncturing by the spark, and means including a distributor for successively connecting the igniting devices in series with said secondary.
- DONALD W. RANDOLPH.
ORA S. DUFFENDACK.
RALPH A. WOLFE.
LEWIS B. HEADRICK.