US2899632A - Electronic ignition system - Google Patents

Description

8- 1959 H. w. LAWSON, JR 2,899,632

ELECTRONIC IGNITION SYSTEM Filed Feb. 20, 1956 27 INVENTOR. V HARRY W LAWSON, JR. BY M ATTORNEY /T ELECTRONIC IGNITION SYSTEM Harry W. Lawson, Jr., Avon, N.Y.

Application February 20, 1956, Serial No. 566,678

7 Claims. (Cl. 323'58) The present invention relates to ignition systems for internal combustion engines, and particularly to ignition systems for automotive engines.

The ignition system commonly in use today is of the single coil interrupter type. This system is based upon the principle that the interruption of current through a transformer induces a voltage in the primary winding of the transformer proportional to the inductance of the primary coil and the rate of change of current in that coil, and induces a voltage in the secondary winding of the transformer equal to the voltage induced in the first winding multiplied by the turns ratio of the two windings.

This system operates well enough except that it is rough on the contacts that do the interrupting, because the contacts have to carry the entire ignition current. The system is simple and reliable, but fails in many ways to meet the requirements of modern, high-speed engines. During the relatively slow initial voltage buildup, needed coil energy is expended through ground leakage paths in the high voltage wiring. In addition, this slow buildup time, although of no consequence at low speeds, amounts to 2.4 crankshaft degrees at 4000 r.p.m. In an effort to correct this, automatic distributor advance has been provided, but nonetheless the difference between the optimum and actual firing points increases with speed. Of the most importance, however, is the inability of the present system to function at high engine speeds. The reason for this is the relatively slow rise time of the charging current in the coil, this time being proportional to the ratio of the coil primary inductance to the circuit resistance. Thus, for proper ignition voltage at high speed, the closed point time, or dwell time, in seconds should be in the order of ten times the time constant for the cycle. The condition has been improved by the addition of another set of points whose function is solely that of increasing the dwell time in order that the charging current may more nearly reach its full value before break.

One object of the present invention is to provide an ignition system which will result in smoother operation of the engine, better high-speed acceleration, and increased life ofthe. points.

Another object of the invention is to provide an ignition system in which a higher voltage may be generated than now is attainable with the conventional breaker and coil system alone.

Another object ofthe invention is to provide an ignition system with greatly increased firing rate capability, and faster rise in. ignition voltage with the result that the ignition system is less effected by high tension leakage losses, and has extremely long breaker point life due tolower voltagev and lower current carrying reqirements.

Other objects of the invention are to provide an improved ignition system which is reliable, has no speed limitation, is unaffected by secondary loading, requires no Warmuptime, has no supply voltage restriction, is of low-cost, and of. easy. service-ability.

nited States Patent ice A further object of the invention is to provide an ignition system having decreased firing delay and a fast rise time. This results in an effective spark advance at high speed with better engine performance.

Another object of the invention is to provide an ignition system which has the advantages above noted, and also the ability to be converted back to the conventional coil and breaker system in event of component failure.

Still another object of the invention is to provide an ignition system which may be used, also, for determining the engine speed, that is, as a tachometer.

Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims.

In the drawing:

Fig. 1 is a simplified electrical diagram of an ignition system constructed according to one embodiment of this invention;

Fig. 2 is a fragmentary wiring diagram illustrating how this system may be used to operate a tachometer; and

Fig. 3 is a diagram of an ignition system built according to another embodiment of this invention.

Referring to Fig. l, the system here shown comprises a source 10 of DC. current, such as the conventional battery of an automotive vehicle. The battery is connectable through the standard ignition switch 11, lines 12 and 14 with the primary winding 15 of the conventional ignition coil or transformer 22, which is in turn connected by the lines 16 and 17 with the shiftab'le contact 18 of a conventional relay 21, having two additional shiftable contacts 19 and Zti. 24 denotes the fixed and 26 the moving contact of the conventional interrupter of the conventional ignition system. The interrupter is denoted as a whole at 25. The interrupter is connected in conventional manner through line 27 with ground.

The primary winding 15 of the ignition coil 22 is also connected by line 16 with a condenser 30 which is connected by line 31, contact 19 of the relay 21, and line 32 with ground. The secondary winding 35 of the ignition coil 22 is connected in conventional manner through a line 36 to the conventional rotor assembly of the automobile.

This part of the apparatus operates, when it is functioning, in conventional manner so that when the primary circuit is opened and closed by the action of the interrupter, a very high electromotive force is induced into the secondary winding 35 and through the line 36 and the distributor to the spark plugs.

The present invention involves use of an auxiliary, additive circuit for operating the ignition system. This auxiliary, additive circuit becomes effective after a slight time delay after closing the ignition switch. This auxiliary circuit is connected by a switch 40 with the line 12 that leads to the battery 10. Switch 40, when closed, connects the battery through line 41, fuse 42, and line 43 with the coil 44 of the relay 21. This coil is connected by line 46 with the contact 47 of a time delay 50. Contact 47 is connected by line 51 with ground. The time delay includes the coil 52 which is connected by line 53 with contact 20 of relay 21, when that contact is in the position shown in Fig. l. The coil 52 is connected by line 54 with line 43.

66 denotes a conventional thyratron. The plate 61 of this thyratron is connected by the lines 62 and 63 with a rectifier 64, which may be a diode rectifier, which is in turn connected by line 65 with a standard inductor 66. The inductor 66 in turn is connected by the line 67, a jumper 68, and the line 69 with the output of a DO. power supply unit 70. The cathode 71 of the thyratron is connected with ground and also by a line 72 with a diode rectifier 74 which in turn is connected by line 75 with line 63.

The triggering coil 86 of the thyratron is connected by a line 81 with the secondary winding 82 of a transformer 85. This seondary winding is connected in turn .by a line 83 with the bias voltage of power supply unit 70. This power supply'unit is connected by line with ground, and by line 87 with the battery when the switches 11 and 40 are closed.

The primary winding 90 of the transformer 85 is connected by line 91 with the line 14, and is connected by line 92 with a resistance 93, which in turn is connected by line 94 with the terminal 95 of the relay 21.

Line 63 is connected to the terminal 97 of the relay The operation of the circuit described is as follows: 'When the conventional ignition switch 11 of the vehicle is closed, and the manually operable disabling switch 40 is closed, current flows from the battery 11} through the switch 11, line 12, switch 40, line41, fuse 42, lines 43 and 54, coil 52, line 53, and contact 21) to ground, starting operation of the time delay 50. At the same time current flows from the battery through the ignition switch 11, line 12, line 14, primary winding 15 of the ignition coil 22, line 16, line 17, contact 18, and line 23 to the contact point 24. As the conventional cam of the interrupter 25 rotates, then, the contact 26 alternately makes and breaks contact with the contact 24, causing the voltage to be induced in the secondary winding 35, and causing high voltage to be applied to the spark plugs. The condenser 34 operates in conventional manner at this time to give the points time to increase their gap above breakdown voltage.

With the contacts 18, 19 and 29 of the relay 44 in the positions shown, the ignition coil 22 is thus excited in the normal manner by operation of the interrupter 25. When coil 52 of the time delay 50 closes the contact 47, however, the relay coil 44 is energized, causing the contacts 18, 19 and to be shifted to close contact with the terminals 95, 97 and 45, respectively.

The contact 20, when in engagement with terminal 45, locks the circuit to the relay coil 44, and breaks the circuit to the coil 52 of the time delay relay 50. The shift of the contact 18 into engagement with the terminal 95 transfers the connection of the stationary contact 24 of the interrupter 25 from the primary winding 15 of the ignition coil 22 to the primary winding 90 of the triggering transformer 85. Resistor 93 is a current limiting resistor. Contact 19, when shifted into engagement with terminal 97, places the condenser 30, as soon as the thyratron becomes conductive, in series with the battery 16, the primary Winding 15 of the ignition coil 22, and through lines 63 and 62, plate 61 of the thyratron 6t and cathode 71 of the thyratron with ground.

After shift of the contacts 18, 19, and 20, then, into contact with terminals 95, 97 and 45, as the contact 26 I of the interrupter 25 makes and breaks contact with the contact 24 of the interrupter, the primary winding 91 of the triggering transformer 85 will induce a sufficient voltage into the secondary winding 82 of this transformer, to trigger the thyratron. Thereupon the circuit to the primary winding 15 of the ignition coil 22 will be closed, inducing high voltage current in the secondary winding of the ignition coil.

The voltage transmitted to the primary winding 15 of the ignition coil 22 from the condenser or capacitor 30 wlll depend, of course, upon the charge in the condenser. The charge from the condenser is obtained from the power supply unit 70 through the line 69, jumper 68, line 67, charging inductor 66, line 65, rectifier diode 64, line 63, contact 19, and line 31. The thyratron 60 is actuated by the secondary 82 of the transformer 85 each time the contacts 26, 24 close. The condenser or capacitor 30 receives a charge approximately twice the voltage sup- 'plied' by the power supply unit 70, due to the resonant circuit charging of the condenser and to the'action of the diode 64.

Cir

When the interrupter 25 opens, a positive trigger pulse is applied by the trigger transformer to cause the thyratron 60 to go into conduction. This causes the capacitor or condenser 30 to be discharged, as described, through the series circuit consisting of the battery 10, primary winding 15 of the ignition coil 22, and the thyratron 60. Since the capacitor or condenser 30 and the primary winding 15 form an oscillatory circuit, the voltage on the capacitor or condenser 30 reverses its original polarity and discharges again on the remaining half cycle through the series loop consisting of the battery 10, the primary winding 15, the inverse diode 74, line 72 and ground. During this latter half cycle, the voltage across the thyratron 60 becomes negative thereby extinguishing the thyratron. As soon as the thyratron is extinguished, the capacitor or condenser 30 is again charged through the charging inductor 66 and the rectifier 64 to its normal charging voltage. The maximum repetition firing rate is determined by the inductor 66 and the capacitor or condenser 30. The charging inductor 66 has a much greater inductance than the inductance of the primary winding 15 of the ignition coil 22.

The current flowing through the jumper 68 varies directly with the number of times per second that the thyratron fires. If a DC. milliammeter is inserted in place of the jumper 68, then, as shown diagrammatically in Fig. 2, the current measured will be a direct function of the number of times per second that the condenser 30 is discharged through the thyratron 60. Therefore, by calibrating this meter in terms of revolutions per minute, an engine speed indicator or tachometer is obtained.

A slight modification of the invention is shown in Fig. 3. This provides better triggering of the thyratron. Here, a limiting resistor is put into the triggering circuit from the secondary winding 82 of the triggering transformer 85. Here, also, both the diode rectifier 64 and the reverse diode rectifier 74 are connected with the condenser 30 through the terminal 97 and contact 19 after contact 19 is shifted by operation of the time delay 50 and relay coil 44.

The thyratron employed may be a tetrode which means that some flexibility in thyratron biasing is obtained. The only requirement for the thyratron is that it be biased either on its control grid 80 or its screen grid 71 to hold ofi the voltage that appears on its plate 61 until such time as the positive trigger pulse appears on its control grid 80 to fire the thyratron in coincidence with the opening of the interrupter 25.

In Fig. 3, the resistors 105 and 106 are limiting resistors.

The switch 40 can be used to disable the electronic system of operation and hence, to put the conventional breaker ignition coil 22 into operation.

If the thyratron 60 should fail by going into continuous full conduction, this would present a short circuit in the line from the power supply unit 70 causing the fuse 42. to open automatically, again returning the system to the conventional interrupter and primary winding circuit.

With the present invention, the efiiciency of the ignition circuit can be raised 100%. This is brought about by the utilization of the energy storage in the inductance of the charging reactor 66 during conduction. Since the capacitor 30 is charged by both the power supply from the battery 10 and the stored inductor energy from the inductor 66, the resultant peak capacitor voltage is approximately twice the power supply 'voltage. The selenium rectifier 64 is used to hold the capacitor at full peak voltage before firing. Since the thyratron conducts for only one half cycle, as soon as the tube extinguishes, its plate voltage drops. This is due to the negative charge left on the capacitor 30. By use of the inverse diode 74, the other half cycle of oscillation is completed, and the firing capacity is charged to twice power supply voltage. again f m approximatel mund potential. It

should be noted that the time of recharging the capacitor 30 is determined by the resonant circuit consisting of the charging inductor 66 and the firing capacitor 30 itself. With proper components the recharging time is in the order of one millisecond. This time on an eight cylinder engine corresponds to over 10,000 r.p.m.

With the present invention power requirements are quite reasonable since operation at as high as 1,000 pulses per second requires only 100 ma. at 250 volts. The transformer 85 supplies the trigger to the thyratron grid as the points open. This then fires the thyratron, discharging the condenser through the coil.

The time delay relay and the relay 44 are wired in a latching manner so that the thyratron cathode protection is maintained under all possible conditions.

During the warm-up interval the relay 50 operates to switch the capacitor 30 to provide conventional ignition When starting. This eliminates any problem with low plate voltage during starter engagement, as well as eliminating any inconvenient starting delay.

With the ignition system of the present invention a higher voltage may be generated for an internal combustion engine ignition system than now exists with the conventional breaker and coil system alone. Moreover, there will be greatly increased firing rate capability, and a faster rise in ignition voltage, with the result that the system will be affected less by high tension leakage losses. Moreover, extremely long breaker point life will be attained because the actual ignition current is controlled by the electronic valve; and the voltage and current through the contacts then is the much lower voltage and current required for triggering the valve. Furthermore, in event of component failure the ignition system will still work because it will return to the conventional system. Still further there Will be decreased firing delay, which means fast rise time, resulting in an effective spark advance at high speed With better engine performance. Still further the system provides a method for determining engine speed, when coupled to a milliammeter, thereby providing a tachometer for the engine speed.

The system according to the present invention can be installed in any car having a conventional ignition system. Installation is mostly a matter of finding a mounting spot in the engine compartment and making the necessary interconnections. The only distributor modification necessary is the removal of the capacitor contained therein.

With the system of the present invention much improved acceleration will be attained, particularly at speeds about 40 m.p.h. The system is also very tolerant of fouled and dirty spark plugs. Some improvement in gasoline mileage is also attained.

While a triggering transformer is illustrated as the means for firing the thyratron, it should be understood that the thyratron tube can be fired by any device that is synchronous with engine timing. As an example, the thyratron could be fired by a magnetic pick-up attached to the distributor shaft in order that contacts may be eliminated.

While the invention has been illustrated, then, in connection with a specific embodiment thereof, and a specific use therefor, it will be understood that it is capable of further modification; and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention, and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains, and as may be applied to the essential features hereinbefore set forth, and as fall within the scope of the invention or the limits of the appended claims.

Having thus described my invention, what I claim is:

1. An ignition system for an internal combustion engine, comprising a source of electrical energy, a transformer, a capacitor, an electronic valve controlling opening and closing of a series circuit in one direction between said capacitor, said transformer, and said source of electrical energy, a resonant charging inductor, a rectifier disposed between said inductor and said capacitor, means for normally connecting said source of electrical energy, said inductor and said rectifier in series circuit to said capacitor to charge said capacitor, means separate from said source of electrical energy for charging said inductor when said electronic valve is conductive, an interrupter operable by said engine for rendering said electronic valve alternately conductive and non-conductive, and means for forming a series circuit in the opposite direction between said capacitor and said transformer when said electronic valve is non-conductive.

2. An ignition system for an internal combustion engine, comprising a source of electrical energy, a transformer, a capacitor, an electronic valve controlling opening and closing of a series circuit in one direction between said capacitor, said transformer, and said source of electrical energy, a second transformer for triggering said electronic valve to render it conductive, an interrupter operable by said engine for operating said second transformer, a second source of electrical energy, a resonant charging inductor, means connecting said inductor to said second source of electrical energy to charge said inductor when said electronic valve is conductive, means including a rectifier for connecting said inductor to said capacitor to charge said capacitor when said electronic valve is non-conductive, and means for forming a series circuit in the opposite direction between said capacitor and said transformer when said electronic valve is nonconductive.

3. An ignition system for an internal combustion engine, comprising a source of electrical energy, a transformer, a capacitor, an electronic valve controlling opening and closing of a series circuit between said capacitor, said transformer, and said source of electrical energy to discharge said capacitor into said transformer when said electronic Valve is conductive, and means including a first rectifier for forming a series circuit between said capacitor, said transformer, and said source of electrical energy in the opposite direction when said electronic valve is non-conductive, a second transformer for triggering said electronic valve to render it conductive, an interrupter operable by said engine for operating said second transformer, a second source of electrical energy, a resonant charging inductor, means connecting said second source of electrical energy to said inductor means including a second rectifier for connecting said inductor to said capacitor to charge said capacitor when said electronic valve is non-conductive, and means including said first rectifier for connecting said capacitor to said electronic valve to extinguish said valve during reversal of the series circuit between said capacitor, said transformer, and the first-named source of electrical energy.

4. An ignition system for an internal combustion engine comprising a source of electrical energy, a transformer having primary and secondary windings, an interrupter operable by the engine for alternately connecting and disconnecting said primary winding to said source of electrical energy to operate said transformer, a capacitor, an electronic valve, and means operable after said interrupter has been connected for a predetermined length of time to said primary winding for disconnecting said interrupter from said primary winding and connecting it to said electronic valve to render said valve alternately conductive and non-conductive, and means for connecting said capacitor in series circuit with said primary winding when said valve is conductive.

5. An ignition system for an internal combustion engine, comprising a source of electrical energy, a transformer having primary and secondary windings, and means for operating said transformer comprising an interrupter operable by the engine for alternately connecting and disconnecting said primary winding to said source of electrical energy, and separate means for operating said transformer comprising a capacitor, an electronic valve operable when conductive to connect said capacitor to said primary winding, and means for connecting said interrupter to said electronic valve for alternately rendering said valve conductive and non-conductive, and a time delay operable when said first-named transformeroperating means has been in operation a predetermined length of time to render said first-named transformeroperating means inoperative and to render said secondnamed transformer-operating means operative. i

6. An ignition system for an internal combustion engine comprising a source of electrical energy, a transformer having primary and secondary windings, a resonant charging inductor, a rectifier, and a capacitor, means for connecting said source, said inductor, said rectifier, said capacitor, and the primary winding of the transformer in series, an electronic valve, means operated by the engine for rendering said valve alternately conductive and nonconductive, said valve when conductive shunting said capacitor and said primary winding into a separate series circuit in one direction with said primary winding, and means for forming a series circuit in the opposite direction between said capacitor and said transformer when said valve is non-conductive.

7. An ignition system for an internal combustion engine, comprising a source of electrical energy, a transformer, a capacitor, an electronic valve controlling opening and closing of series circuit between said capacitor, said transformer, and said source of electrical energy to dis charge said capacitor in one direction into said transformer when said electronic valve is conductive, and means including a first rectifier for forming a series circuit in the oppositedirection' between said capacitor and said transformer when said electronic valve is non-conductive, means for triggering said electronic valve to render it conductive, a resonant charging inductor, means connecting said source of electrical energy to said inductor, means including a second rectifier for connecting said source of electrical energy to said capacitor to charge said capacitor when said electronic valve is non-conduc tive, and means including said first rectifier for connecting said capacitor to said electronic valve to extinguish said valve during reversal of the series circuit between said capacitor and said transformer.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES The General Electric Review, vol. 32, No. 7, 1929, p. 398, article by Hull.

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