US2901670A

US2901670A - Ignition system

Info

Publication number: US2901670A
Authority: US
Publication date: 1959-08-25
Anticipated expiration: 1976-08-25

Description

Aug- 25, 1959 D. E. sUNsTElN IGNITION SYSTEM Filed Jan. 24, 1956 fill' vl wr 0 cJ 7 NN 7 my a WJ 5 u W m m United States Parent() IGNITION SYSTEM David E. Sunstein, Bala-Cynwyd, Pa., assigner to Philco Corporation, Philadelphia, Pa., a corporation of Penn- Sylvania Application January 24, 1956, Serial No. 560,976

2 Claims. (Cl. S15- 200) This invention relates to ignition systems, and while the invention is applicable particularly to ignition systems for automobles, it is intended to be employed wherever it may find useful application.

Due to the fact that most of the present day automobile engines have eight-cylinder engines with high compression ratios frequently in excess of 7.5 to 1, a problem has arisen with respect to the stringent ignition requirements of such engines. Optimum perforance cf such engines can be attained only by supplying to the spark plugs an extremely high voltage greatly in excess of that which was suitable for prior engines having lower compression ratios. The reason for this is that with higher cornpression ratios, the breakdown strength of the gasoline mixture is increased. Moreover, greater engine eflciency through use of leaner mixtures can be achieved if the spark plug gap is increased to give optimum performance, and this also leads to the need for even higher voltage. The spark-creating voltage must be maintained high to assure reliable firing of the spark plugs even when the plugs are fouled to a considerable degree, e.g. to a resistance of 100,000 ohms, which can result from sustained low horsepower use. Generally speaking, it is desirable to provide a voltage of about 30-kv. across each spark plug, even when it is fouled to show a shunt resistance as low as 100,000 ohms.

The problem is to convert the low D.C. voltage of the battery into a very high voltage pulse. If this is done in a very short period of time, a reduced amount of energy may be employed with each actuating spark, since a rapid build-up of high voltage causes breakdown before there is heavy energy loss in the shunt resistance of the plug. Moreover, it is desirable to maintain the current through the breaker points low to avoid intolerably rapid deterioration of the points. For example, it is desirable to provide at the spark plugs a voltage pulse having a rise time of about l to 3 microseconds and having a peak voltage of about 30-kv., and at the same time limit the lcurrent through the breaker points to about 4 amperes. Moreover, it is desirable to keep the peak voltage across the breaker points small (no more than about 250 to 350 volts), to prevent energy loss in possible arcing in the open breaker point air-gap. For the same reason it is desirable to prevent the voltage across the breaker points from rising too rapidly when they are lirst opened. There vis moreover the problem created by eight cylinder engines of providing less time to store energy from the battery when the breaker points are closed, than is provide-d with 6 or 4 cylinder engines.

All these factors have combined either to reduce the reliability of previously devised ignition systems, necessitating frequent change of components with life, or to excessively complicate the mechanism, leading to high initial cost.

It is well known that a voltage pulse may be produced, in an ignition system, by storing energy from the low voltage battery in the magnetic iield of an inductor, then transferring the stored energy to a storage capacitor, and

2,901,670 Patented Aug. 25, 1959 nally discharging the capacitor into a device such as a transformer to produce the desired voltage pulse. The operation involves relatively slow accumulation of energy from the battery, transfer of the accumulated energy to the storage capacitor, and veryV rapid discharge of the energy so as to produce a voltage pulse of short duration. While systems of this type have been proposed heretofore, such prior systems are not entirely satisfactory for use with modern high compression engines. The principal reason for this is the inability of such prior systems to so control the discharge of the storage capacitor that the discharge invariably takes place when, and only when, all of the accumulated energy has been transferred to the capacitor. Since the amplitude of the voltage pulse is dependent upon the amount of energy discharged from the storage capacitor, the maximum pulse amplitude can be attained in each operating cycle only by insuring that the discharge of the capacitor will take place when the energy stored in the capacitor is a maximum. Prior systems have not provided this insurance, and when it is considered that the voltage of the battery may vary and thus cause some variation of the stored energy, it may be realized that maximum utilization of the stored energy is all the more improtant. Premature -discharge of the storage capacitor may result in a relatively weak voltage pulse. As far as is known, none of the prior proposed systems have been suciently satisfactory for commercial use.

Y Accordingly, one object of the present invention is to overcome the deficiencies of prior systems and to provide an improved ignition system which will give optimum performance of modern automobile engines having very high compression ratios.

Another object of this invention is to provide an ignition system, of the general character above mentioned, Iin whichprepetitive production of a very .high voltage pulse is assured. y

Another object of the invention is to provide an ignition system which will reliably re wide gap plugs, even though the insulator thereof be considerably fouled.

A further object of the invention is to provide an ignition system enabling increased fuel economy.

A further object of the invention is to provide such a system which is simple in construction and therefore ycapa-ble of low-cost manufacture.

Other objects and features of the invention will be apparent from the description to follow.

In accordance with this invention, there is provided a system of the type above mentioned in which energy is stored in the magnetic field of anV inductance device and is transferred to a storage capacitor, and there is further provided in such system a novel arrangement for assuring that the discharge of the capacitor shall take place only when substantially all of the accumulated energy has been transferred to the storage capacitor. More particularly, there is provided an arrangement whereby the discharge of the storage capacitor is caused to take place in response to reversal of polarity of the voltage across 4an inductor, such reversal taking place only when substantially all of the energy has been transferred to the capacitor. In this way, it is assured that during each operating cycle, a voltage pulse Vof maximum amplitude will be produced.

The preferred embodiment of the invention, as hereinafter described, employs tw'o transformers, one for storage of energy from the battery and the other for production of the voltage pulse from the discharge of the storage capacitor. In such a system, the transformer windings may be self-tuned, i.e., tuned by their respective distributed capacitances, in such manner as to enhance theV energy transfer Wherever this `is found desirable, although it is not essential.

.embodiment of the invention; and

Figs. 2 to 4 are explanatory illustrations Yof the'principal voltages which are developed at'certain points in the system.

Referring more particularly toV Fig. l, the usual automobile battery is shown at'10 and the usual breaker points are represented at 11, the latter being shunted by ythe usual condenser 12. The inductance device for storing energy from the battery is preferably a transformer 13 whose primary winding 14 is in series circuit with the battery and the breaker points, although the energystorage device could be a simple inductor. The breaker points serve to recurrently close and open the primary circuit, thereby to effect recurrent storage of energy in the transformer. A storage capacitor 15 is connected to the secondary winding 16 of the transformer to receive energy from the transformer upon each opening of the primary circuit. A unilaterally-conductive device 17, preferably in the form of a diode, is connected between the secondary winding 16 and the capacitor 15, and is poled so as to permit charging of the capacitor and to prevent discharging thereof into the secondary winding 16.

Control of the discharge of the storage capacitor 15 is eected by means of a normally non-conductive device 18, which preferably is an arc device and which is serially included in the discharge circuit for the storage capacitor, the latter circuit also preferably serially including the primary winding 19 of an output transformer 20. The arc device 18 has two

main electrodes

21 and 22, and a starting electrode 23 which is connected to the lower end of the secondary 16 of transformer 13. The spacing between

electrodes

21 and 22 is such that conduction by device 18 can only be initiated by application of a starting voltage to the starting electrode 23. Such conduction is effected by the reversal of polarity of the voltage across secondary 16, which reversal takes place due to the fact that the secondary winding 16, together with its distributed capacitance 24, forms an effective resonant circuit. When the discharge of capacitor 15 takes place, the energy stored therein is quickly transferred through the output transformer to the distributed capacitance 25 effectively connected across the secondary 26 and resulting from the capacitance of high voltage wiring, the distributor, and the spark plug activated through the distributor.

Considering in greater detail the operation of the system, during the interval when the breaker points 11 are closed, energy is stored in the magnetic lield of transformer 13 from battery 10 at a relatively slow rate, the current through the breaker points being sufficiently low so as not to cause excessive deterioration of the points. When the breaker points open, a positive voltage is applied to the anode of the diode 17, and the diode conducts and effectively closes the charging circuit to the capacitor 15. At this time there is no appreciable voltage between

electrodes

21 and 23 and the arc device 18 is nonconductive. The energy stored in transformer 13 is therefore transferred to the storage capacitor 15 and the latter charges as shown by the rising portion 27 of the curve in Fig. 2. Substantially all of the energy that was stored in transformer 13 is transferred to capacitor 15 within approximately 1A cycle of oscillation at the resonant frequency of the

elements

15 and 16.

During the charging of capacitor 15, the voltage across -the secondary winding 16 rises, as shown by the rising portion 28 of the curve of Fig. 3, the lower end of the winding being positive. When substantially all of the energy has been transferred to capacitor 15, the voltage across winding 16 swings abruptly negative, -asv shown by portion 29 of the curve of Fig. 3. This is due to the fact that winding 16 and its distributed capacitance 24 form an elfective resonant circuit, and the voltage across the winding oscillates at the resonant frequency of said circuit as shown in Fig. 3, although only the solid line portion 29 of the curve is of interest here. The voltage swings to a negative peakY substantially equal to the original positive peak and cuts olf the diode 17, preventing discharge of capacitor 15 into the winding 16. At the same time, a negative voltage pulse, as shown at 30 in Fig. 4, is applied between the starting electrode 23 of the arc device 18 and the discharge electrode 21 thereof, and initiates conduction thereby.

The capacitor 15 now discharges rapidly into the primary 19 of transformer 20, and the energy that was stored in capacitor 15 is transferred through transformer 20 to the distributed capacitance 25. Consequently a high voltage pulse is developed across distributed capacitance 25 and causes firing of one of the spark plugs.

As the capacitor 15 discharges, the voltage thereacross decreases as shown by the portion 31 of the curve of Fig. 2. Immediately following the full charging (top of line 27 of Fig. 2) of capacitor 15, the breaker points 11 may close to again store energy in the transformer 13 and thus initiate the next operating cycle.

From the foregoing description, it will be seen that maximum amplitude of the voltage pulse produced by discharge of capacitor 15 is assured, inasmuch as the discharge is not permitted to take place until substantially all of the energy stored in transformer 13 has been transferred to capacitor 15. `Thus,' during each and every operating cycle, a very high voltage pulse is supplied to one of the spark plugs. Therefore the system is particularly well adapted for use with modern high compression engines and will assure optimum performance of such engines. Actual tests of the system have proved that it enables attainment of optimum performance of such engines.

By way of example only, in one physical embodiment of the system the following values are employed.

Primary winding 14 5.5 mh. Secondary winding 16 10 mh. Coeicient of coupling of windings 14 and 16 .756.V Capacitor 15..V 2,000 micro-microfarads. Primary winding 19 5.7 mh. Secondary winding 26 11 mh. Coefiicient of coupling of

windings

19 and 26 .6 Distributed capacitance 25 50 micro-miorofarads.

In the same embodiment a V12-volt battery is employed, a two-ohm resistor is included in series with the battery, a .5 microfarad condenser is employed across thebreaker points, vand a 1.8 megohm resistor is employed in series with the starting electrode 23 ofthe arc device 18' As hereinbefore mentioned, the transformer windings may be self-tuned, if desired, in a manner to enhance energy transfer. For example, the secondary of each transformer may be self-tuned to a subharmonic of the frequency to which the primary is self-tuned, so as to obtain an additive effect. In one physical embodiment, the secondary of transformer 13 was tuned to the seventh subharmonic of the resonant frequency of the primary, and the secondary of transformer 20 was self-tuned to the second subharmonic of the resonant frequency of the primary.

While a preferred embodiment ofthe invention has been illustrated and described, it is to be understood that the invention is not limited thereto but contemplates such modifications and other embodiments as may occur to those skilled in the art.

I claim:

l. In an ignition system, a source of relatively low D.C. voltage, an energy-storage device including an inductor which together with its distributed capacitance 5 :forms an effective resonant circuit having a relatively high resonant frequency, a circuit interconnecting said source and said device, means for recurrently closing and opening the llatter circuit to eiect recurrent storage of energy from said source in said device, a capacitor connected to said inductor for transfer of said energy to the capacitor, said inductor and said capacitor forming a resonant circuit having a substantially lower resonant frequency than the rst-mentioned resonant circuit, a unilaterally-conductive device connected between said inductor and said capacitor and poled so that transfer of energy to said capacitor takes place in response to opening of said interconnecting `circuit at a rate determined by the resonant frequency of said ind-uctor and said capacitor, the iirstmentioned resonant circuit causing abrupt reversal of polarity of the voltage across said inductor Vwhen substantially all of the energy has been transferred to said capacitor, a discharge circuit connected to said capacitor, an arc device in said discharge circuit connected to the junction of said unilaterally-conductive device yand said capacitor, said arc device having a starting electrode, means connecting said starting electrode to the junction of said inductor and -said unilaterally-conductive device to initiate discharge of said capacitor in response to the 6 aforementioned labrupt reversal of polarity of the voltage across said inductor, and means responsive to the discharge of said capacitor for producing a high voltage pulse.

2. An ignition system according to claim 1, wherein said inductance device and said means for producing a thigh voltage pulse are transformers each having selftuned primary and secondary windings, and wherein the secondary wind-ing of each transformer is self-tuned to a subharmonic of the frequency to which the primary winding is self-tuned to enhance the energy transfer therethrough.

References Cited in the le of this patent UNITED STATES PATENTS 2,027,617 Randolph Jan. 14, 1936 2,030,228 Randolph et al Feb. 11, 1936 2,203,579 Randolph June 4, 1940 2,416,971 Welch et al. Mar. 4, 1947 2,447,377 Tognola et al. Aug. 17, 1948 2,651,005 Tognola Sept. 1, 1953 FOREIGN PATENTS 529,558 Great Britain Nov. 22, 1940