US2475994A - Ignition system - Google Patents

Description

July 12, 1949. H, RT 2,475,994

IGNITION SYSTEM Filed May 14, 1946 FLA TE CRIT CAL 1/0477! 6 E LINE .5 00

GRID VOLTAGE 5&7. Z

Patented July 12, 1949 UNITED STATE$ PATENT IGNITION SYSTEM Brooks H. Short-,Anderson, Ind., assignorto General Motors Corporation, Detroit, Mich., a corporation of Delaware Application May 14, 1946, Serial No. 669,499

1 Claim.

This invention relates to ignition apparatus for igniting liquid fuel, for example, a gasoline burner.

An object of the invention is to provide ignition apparatus which operates without the use of contact circuit-make-and-break devices to provide a-rapid succession of ignition sparks. In the disclosed embodiment of the invention, this object is accomplished by an ignition coil having a secondary winding connected with a spark gap and having a primary winding, a capacitor to be intermittently discharged through the primary winding, a thyratron tube operative to establish a circuit between the capacitor and primary winding when, corresponding to a certain negative bias on the tube grid, the tube plate voltage grows to a certain value whereby the condenser is discharged through the primary winding and the tube becomes non-conducting, a current source or power supply for plate and grid voltages and for capacitor charging, and circuit connections between the power supply and the tube and capacitor providing-for a predetermined negative grid bias and for the concurrent growth of voltage at the capacitor and" tube plate.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing, wherein a preferred embodiment of the'present invention is clearly shown.

In the drawing:

Fig. 1 is a diagram of the embodiment of the invention.

Fig. 2 is a chart showing the characteristics of a thyratron used in the system.

Referring to Fig 1, a storage battery or other current source In which is grounded is connected by a switch II with the center tap l2 of a primary I3 of a transformer l5 having a secondary l4 provided with a center tap I6 and having its end leads connected with a capacitor C1. The end leads of primary l3 are connected with contacts 22 and 24 of a vibratory rectifier having a vibratory reed 25 carrying a contact 23 which vibrates between contacts 22 and 24 and alternately engages them. The end leads of transformer secondary I4 are connected with vibratory contacts 26 and 28 between which there vibrates a contact 21 carried by the reed 25. Contact 21 alternately engages contacts 26 and 28 concurrently with the alternate engagement of contact 23 with contacts 22 and 24. The reed 25 is maintained in a state of vibration due to the operation of an electromagnet having a coil surrounding a core 3| which effects the downward attraction of the armature 29 attached to the reed 25 when switch H is closed. Upon the engagement of contact 23 with contact 24 the coil 30 is short circuited, whereupon the reed is released and its movement upwardly causes contacts 23 24 to engage contacts 22 and 26. When contact 23 separates from contact 24 the short circuit around the coil 30 is interrupted so that the magnetism begins to build up. By the time contacts and 2? have engaged contacts 22 and 25, the magnetism in the coil 3!. is again suflicient to eifect the downward movement. of the armature 29 so as to bring contacts 23 and it"! into engagement with contacts 24 and 28 again. Thus. vibration is maintained so long as switch it is closed. The operation of the Vibrator is to cause current to flow intermittently through the two halves of the primary thereby causing higher voltages to be induced alternately in the two halves of the secondary I A.

is grounded at one end. A capacitor C2 is connested between wire 32 and wire 36. Potentiometer 35 has a slider 350. connected with a wire 31. A. resistance 35 is connected with resistance 34 and with a wire 39 connected withthe plate 4! of a thyratron tube Ml. A capacitor C3 is connected between wire 3'! and, Wire 39.. The wire 36 is connected with the grid 42 of tube 40. The cathode 53 of tube do is connected with primary winding 5! of ignition coil 50, and the other end of said winding is connected with wire 31. The secondary which is grounded at one end is connected at the other with a grounded spark plug 53 for maintaining the combustion of fuel vapor. The cathode heater 44 of thyratron is connected with a transformer secondary 45.

The following electrical dimensions have been found satisfactory:

Primary winding i34l turns #16 gauge wire Secondary winding 14-4000 turns #38 gauge wire Secondary 45--35 turns #22 gauge wire Capacitor Cl.0025 m. f. d., 2000 v.

Capacitor C2-.10 m. f. d., 450 v.

Capacitor C3--.25 m. f. d., 600 v.

Resistance s5-30oo ohms, wire wound Resistance 3450,000 ohms, 2-watt Resistance 3875,000 ohm-s, 2-watt Thyratron 4ll-type 2051 electron tube Transformer a conventional automobile ignition coil Theory of operation All components up to and including C2 make up a power supply. This power supply provides 250 volts of direct current at terminal 33A and 6.3 volts of alternating current. The 250 volts D. C. at terminal 33A provides plate and grid voltages The characteristics of a thyratron of the type used in this device are best shown in the curve of Fig. 2. Any combination of potentials that fall to the left of the critical line will not render the tube conducting. This region is indicated by shading. Any combination falling to the right of the line will cause the tube to become conducting. For example 100 plate volts, and 6 grid volts will not cause conduction (point A). 200 volts plate and 3 volts grid will cause ionization and result in conduction (point B).

In this system, the negative bias Voltage is determined by the setting of the potentiometer 35. Assuming that a represents the resistance between the upper end of 35 and the slider 35a, and

' ionized, and the capacitor C3 again begins to that b represents the resistance from the slider to I the lower end, the grid potential Eg is equal to 250 volts (potential at 33A) times the ratio of re sistance a to the total resistances between, 33A and ground (resistance 34 plus resistance 35) Let it be assumed that the slider 35a is set to give a grid potential E9 of -5 volts with respect to the cathode 43. That is, the grid 42 is 5 volts more negative than the cathode 43. With -5 volts on the grid, the tube 40 will become conducting whenever the plate potential becomes 190 volts. Since plate 4| is directly connected to ca-- pacitor C3 by wire 39, plate voltage grows with the growth of voltage on capacitor C3. The time of growth of voltage upon capacitor C3 is dependent upon the potential between terminal 33A and wire 31 connected with slider 35A, and upon the time constant of the circuit including resistance 38 and capacitor C3. According to their electrical dimensions given heretofore as an example, this time constant is 75,000 (ohms) .25 (m. f. d.) 10- =.01875 seconds. The voltage upon capacitor C3 will grow exponentially until 190 volts is reached. At that point, the critical line is crossed, making the thyratron tube 40 conducting. When such ionization takes place within the tube, the energy stored in the capacitor C3 is discharged through the thyratron, and the ignition coil primary 5|. This discharge sets up flux in the coil core, which in turn produces the high voltage output in the coil secondary 52. When, C3 has been discharged, the tube 40 becomes decharge and the cycle is repeated so long as switches 33 and II remain closed.

Switch II should be closed before switch 33 is closed to allow time for heating the tube 40 before beginning to build up voltage at the capacitor C3 and at the plate 4|.

While the embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claim which follows.

What is claimed is as follows:

An ignition system for providing a rapid succession of sparking impulses comprising an ignition coil having a secondary winding for connection with a spark gap and having a primary Winding, a capacitor to be intermittently discharged through the primary winding, a'thyratron tube operative to establish a circuit between the capacitor and the primary winding when, corresponding to a certain negative bias on the tube grid, the tube plate voltage grows to a certain value whereby the condenser is discharged through the tube and the primary winding and the tube becomes non-conducting, a current source or power supply for plate and grid voltages and for capacitor charging, and circuit connections between the power supply and the tube and capacitor providing for a predetermined negative grid bias and for the concurrent growth of voltage at the capacitor and tube plate, whereby the frequency of sparking impulses is determined by rate of charge and discharge of the capacitor.

BROOKS H. -SHORT.

REFERENCES CITED The following referenlces are of record in the file of this patent:

UNITED STATES PATENTS Germeshausen May 21, 1940

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