US2409202A - Electronic ignition system - Google Patents

Description

Oct. 15, 1946.

O. T. FRANCIS ELECTRONIC IGNITION SYSTEM Filed Dec. 27, 1943 raw Patented Oct. 15, 1946 UNITED STATES PATENT OFFICE 2,409,202 ELECTRONIC IGNITION SYSTEM Oliver T. Francis, Renville, Minn.

Application December 27, 1943, Serial No. 515,654

Claims.

This invention relates to ignition systems and more particularly to booster spark producing means.

In ignition in the cylinder of an internal combustion engine, two problems present themselves. 1. The release of electrons from th cathode terminal of a spark gap. 2. The vaporization of molecules of gasolene from the liquid spray to build up the required vapor pressure to permit ignition.

The reactions involved in both of these problems are Einsteins quantum reactions. 1. The release of an electron from a tungsten cathode requires a quantum of 4.5 electron volts, the energy of a photon of .28 mu wavelength. 2. The vaporization of a molecule of gasolene requires a quantum of .4 electron volts, the energy of a photon of 3 mu wavelength. Both of these problems are extremely aggravated by the low temperatures of cold weather. The radiation of a black body at thirty degrees below zero contains few photons of either of these wavelengths. At low temperatures electrons are not readily released from a metal, such as a cathode tungsten spark gap terminal, and the number of free electrons in the vicinity of the cathode terminal is very much reduced. It therefore requires a higher anode terminal voltage to give the necessary acceleration to the electrons in the gap to release a sufiicient number of positive ions in said gap and to accelerate sai ions to said cathode with sufficient velocity to release the necessary large number of electrons to produce a good spark. The problem of releasing electrons from the cathode terminal is further aggravated by the fact that the cathode is usually covered with a thick carbonized layer which has a higher Work function than the metal from which the cathode is made. The cathode is also usually covered with a congealed insulating coating of cylinder oil. It is an object of this invention to produce a voltage sufliciently high to break through said insulating coating of oil, extract the electrons from the cathode, and to follow this break down voltage with a discharge current sufficient to melt said oil coating over a large portion of said oath ode to render subsequent sparking across said gap more easy.

Another object is to illustrate how the anode of a spark gap may be maintained at a high positive D. C. potential for a period of time before breakdown to evaporize ice and short circuiting detrimental effects for said gap. Another object is, to illustrate a resistance shunted by a con- 2 denser for superimposing a breakdown high voltage on said D. C. potential.

The energy of a spark is L. At high speed the L must not be too large or th current will not have time to build up through theinductance to produce a spark. For starting, however, where the speed of rotation of the motor is very slow, it is desirable to have the L as large as practicable in order to get as much energy as possible into the spark. It is an object of this invention to illustrate an auxiliary inductance coil and means for short circuiting said coil except for starting,

The second above mentioned problem, namely, the building up of required'pressures of gasolene, which is taken into the cyl nder-in the form of liquid spray suspended in the intake air, is readily solved at ordinary temperatures by the heat of compression in said cylinder. However, at low temperatures, this heat of compression is not sufiicient to heat the air and to build up the required vapor pressure in the cylinder, and ignition is therefore impossible, even though, as is usual practice, the motor may be fullytchoked. This choking results in an undue wasteof gasolene, and it is one of the objects of this invention to eliminate this waste.

Sir Humphry Davy early in the nineteenth century discovered that required vapor pressures were necessary to produce ignition between a gas and air. He found that more than six and less than fourteenth volumes of air would explode with one volume of methanewhen ignited, but that outside of those limits ignition would not readily occur.

To produce heat to create the required vapor pressures in the vicinity of the spark gap in cold -Weather, various booster spark systems have been devised. These systems usually take the form of means for interrupting a low voltage ignition coil primary current several times during the period that the distributor brush is making contact with each spark plug in order to produce several sparks at the spark gap instead of just one and thereby multiply the spark heating effect by the number of said sparks. The heat produced at the spark gap by such systems is very small, since, while .03 joules produces a good spark most of the energy i .not dissipated at the spark gap but in the resistance 01' the secondary of the ignition coil. Furthermore, such systems must be operated on a retarded spark in order to prevent back fire. With a retarded spark the heat of compression which may have been considerable at top dead center has been dissipated by the expansion of the air in the cylinder, with the resultant lowering of vapor pressure of gasolene in the cylinder. Even though ignition takes place with such a retarded spark, th power stroke i usually not sufi'icient to turn the crank shaft over several times, and the engine does not start.

It is an object of this invention to produce a large electrical discharge at the spark gap, thereby building up the required ignition vapor pressure of gasolene in the vicinity of said gap, even in extremely cold weather.

Another object is to produce a high voltage pulse to break down a spark gap and by a shunt low impedance path to pass a large current through said spark gap to produce a large dissipation of energy at said gap. Another object is to illustrate a means for breaking down a spark gap, and by a unidirectionally conductive gas discharge device passing a large current through said broken down gap.

The voltage of an automobile battery falls considerably in cold weather, when the starter turns the engine over. With a battery whose no current voltage measures 6.5 volts, the voltage in the battery if new falls below volts, and if it is old it falls to below 3 volts. The new battery then is not able to produce a hot spark, and the old battery is not able to produce a spark at all. It is an object to illustrate how a voltage from the secondary of a conventional ignition coil may be amplified up to produce any desired dissipation of energy at the spark gaps.

These and other objects of the invention will be obvious from the following description, claims, and figures, wherein:

Fig. 1 shows an ignition system incorporating my invention, and

Fig. 2 shows how my invention may be readily adapted to a conventional ignition system with the use of less apparatus than in Fig. 1.

Referring to Fig. 1, a conventional rectifier system 32, drawing power from A. C. lines I0, furnishes power for the ignition system. This rectifier system consists of a rectifier tube 1, having a plate connected to each terminal of the secondary of a stepup transformer 8. The cathode of tube 1 is connected to ground I, and the center tap of the secondary of transformer 8 through condenser 2 in parallel with resistance 3. Rectifier tube 6 has a plate connected to each terminal of secondary of transformer 9. The cathode of rectifier 6 is connected through condenser 4 in parallel with resistance 5 to the center tap of transformer 9 and to the cathode of tube 7.

The cathode of tube 6 is connected through inductance coils I I, and I3 to the plate of vacuum tube I I. The grid of tube IT is connected through resistance to the cathode of rectifier tube I. The cathode of tube I1 is connected to the plate of vacuum tube I8. The screen grid of tube I8 is connected through resistance 2| tocathode of rectifier tube 7. The control grid of tube I8 is connected to a mid-point of voltage divider resistances 31, 38, which resistances are connected across the secondary of conventional ignition coil 34, the primary of which is supplied with current from battery 35 in series with interrupter IS, in parallel with condenser 35 in the conventional manner.

The plate of vacuum tube I! is connected to distributor brush 3| through the anode and cathode of rectifier tube I5. The distributor brush 3|, as it rotates makes contact with a plurality of contacts 29, to ground I through one of spark gaps 22, 23, 24, 25, 26, 21. Distributor brush 3| also is connected to the positive terminal of power supply 32 through a unidirectionally conductive gas discharge device I4 and current limiting resistance 33. The inductance Il may be short circuited by key I2 for purposes hereinafter described.

In operation when interrupter I9 is opened, a current passes from the grounded terminal of secondary of coil 34, through resistances 37, and 38 placing a negative potential on the control grid of tube I8. A high voltage surge is produced between the anode of vacuum tube l1 and ground as described in my U. 8. Patent No.

2,328,444. This surge is passed from the anode to the cathode of rectifier I 5, through distributor brush 3| to one of the contacts 29, 30 and then through one of the spark gaps 22-21 to ground I. One of the spark gaps being broken down, condenser 4 in series with condenser 2 discharges through current limiting resistor 33, gas discharge device !4, distributor brush 3!, and said broken down spark gap to ground I. This shunt discharge current passing through device I4 is many times as large as the break down surge passing through rectifier I5 and is of suflicient value to melt the congealed oil on the terminals of the spark gap, so that the succeeding sparks pass across the gap more readily. This shunt discharge current also builds up the required ignition vapor pressure of gasolene by evaporizing the liquid gasolene spray suspended in the air in the vicinity of the spark gap and ignition takes place in the coldest temperatures.

After starting, key I2 is closed, shorting inductance II, in order to permit production of ignition sparks to take place at a higher rate of speed than would be possible if both inductances i I and I3 remained in the circuit.

To further illustrate the functioning of my device the constants of a circuit used in experimental work are given. It will be understood that my invention is not limited to the circuit values iven or even to values of the same order, the invention being described in the claims.

In this experimental circuit rectifier tubes 6, l wer type 80. Condensers 2 and 4 were 24 microfarads each. Resistances 3, 5 were 200,000 ohms each. Lines I0 were the volt, 60 cycle power lines. Inductances II and I3 were each secondaries of conventional Ford ignition coils 30 henrys). Vacuum tube I l was a type 809. Tube It was a type 2A5. Resistance 2| was 3000 ohms. Resistance 20 was 2000 ohms. Current limiting resistance 33 was 50 ohms. Gas discharge device I4 was a type 866 mercury rectifier. Rectifier I5 was a type 27 (grid and plate connected together). Resistance 3'! was 2500 ohms. Resistance 38 was 10.000 ohms. Ignition coil 34, battery 35. interrupter l9, distributor arm 3|, condenser 36, were those of a conventional six cylinder automobile. When the engine of the automobile was turned over, sparks about 1000 times as large as ordinary sparks could be drawn from the positive terminal of the spark plugs.

Fig. 2 shows how my invention may readily be adapted to the conventional ignition system in common use. Circuit elements performing the same function as those in Fig. 1, have been assigned the same reference numerals.

Referring to Fig. 2, the high tension line 52 was a conventional automobile distributor line. which connected the distributor to spark gap 21, and through said gap to ground I, which was the frame of the automobile. In series with line-'52 was inserted resistance I6, in parallel with condenser 28, The anode of gas discharge device H was connected to the high tension terminal of spark gap 21. The cathode of device [4 was connected to the negative terminal of power supply 32. The positive terminal of power suppl 32 was connected through current limiting resistance 33 to ground I.

When the engine of the automobile was turned over by the starter a high voltage pulse passed from the grounded terminal of the secondary of conventional ignition coil 53, through spark gap Zl', condenser 28, high tension line 52, distributor arm 3!, to the other terminal of the secondary of said ignition coil.

Spark gap 2'! being broken down condensers 2 and 4 discharged through current limiting resistance 33, to ground, through spark gap 21, and gas discharge device I 4. Sparks about a thousand times as large as the conventional sparks could be drawn from the high tension side of spark gap 21. Gas discharge device l4 (an 866) lighted up each time gap 2! broke down, and the discharge current was sumciently large to light up current limiting resistance 33 each time a spark occurred, which resistance in that instance was a 40 watt, 110 volt tungsten filament light.

The energy content of the spark discharge through the circuit including condensers 2, 4,

spark gap 21, gas discharge device M was substantially 1/2CE2- Since condensers 2 and 4 were each 24 microfarads and were connected in series the total capacity was 12 microfarads, The charge on these condensers totalled 700 volts. /2CE X 12 X x49 10 :3 joules.

It is to be further noted that this energy was not dissipated by a high resistance path such as the secondary of an ignition coil but was dissipated to a large extent at the spark gap, From a consideration of the above energy formula it becomes obvious that the energy dissipated at the spark gap for a single discharge can be varied either by varying the capacity of the condenser, or the voltage impressed on said condenser.

In extremely cold weather it was found desirable to heat tube l4 indoors keeping it covered with a woolen covering, as it is well known that an 866 does not function properly when any part of the bulb is below degrees centigrade. Heating this tube by means of an electrical pad also proved satisfactory.

One feature of my invention consists in means for rendering conductive a spark gap by a high voltage pulse, and a low impedance path for passing currents of large amperage through said broken down gap. While I have shown herein, what I believe to be the best form of my invention, various means for producing high voltage pulses are known, and various means for producing a low impedance path for passing currents of large amperage are also known. It is therefore not desired to limit my invention to the apparatus which I have illustrated in detail. My invention is to be limited in scope only as defined in the following claims.

What I claim is:

1. In an ignition system, a first circuit comprising the series connection of a generator of a high voltage positive pulse, the anode and cathode of a spark gap, a second circuit comprising the series connection of an electrical energy storing source of current, the anode and cathode of a gas discharge device, and said anode and cathode of said spark gap, and means for applying said positive pulse to said anode of said spark gap to render said gap conductive and cause current to fioW in said second circuit.

2. In an ignition system, a first circuit comprising a generator of a high voltage positive pulse, a resistance shunted by a condenser, the anode and cathode of a spark gap, a second circuit, comprising the anode and cathode of a gas discharge device, an electrical energy storing source of current, and said anode and said cathode of said spark gap, and means for applying said positive pulse to said anode of said spark gap to render said gap conductive and cause current to flow in said second circuit.

3. In an ignition system, a first circuit comprising the series connection of a generator of a high Voltage pulse, the anode and cathode of a rectifier tube, and the anode and cathode terminal of a spark gap, a second circuit comprising the series connection of an electrical energy storing source of current, the anode and cathode of a second rectifier tube, the anode and cathode of said spark gap, and means for applying said pulse to said gap to render it conductive and cause current to fiow in said second circuit.

4. In an ignition system, a first circuit comprising the series connection of a high voltage pulse generator, a resistance shunted by a condenser, a distributor, one of a plurality of spark gaps, a second circuit comprising the series connection of an electrical energy storing source of current, the

anode and cathode of a rectifier, said distributor and said spark gap, and means for applying said high voltage pulse to said spark gap to render said first circuit conductive and cause current to flow in said second circuit.

5. In an ignition system, a first circuit comprising the series connection of a generator of a high voltage pulse, the anode and cathode of a spark gap, a second circuit comprising the series connection of an electrical energy storing source of current, the anode and cathode of a rectifier, and said anode and cathode of said spark gap, and means for applying said ulse to said anode of said spark gap to render said gap conductive and cause current to flow in said second circuit.

OLIVER T. FRANCIS.

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