US2475995A - Ignition system - Google Patents

Description

B. H. SHORT IGNITION SYSTEM July 12, 1949.

Filed OCC. ll, 1946 Patented July 12, 1949 IGNITION SYSTEM Brooks Short, Anderson, Ind, assignor to GeneraliMotors Corporation, Detroit, Mich, a corporation ofDelaware Applicationioctober 11, 1946, SerialNO. 702,869

4Claims. 1

This invention relatesto-..-high.frequency jgnition systems for internal-combustion engines.

An object of the presentinventionis to obtain a rapid succession or shower of sparks during-the period of closureof the-engine operated: timer contacts. This object is accomplished by'the combination of a resonator connected-with thespark plug, an oscillator inductively connected with the resonator and having a tube; a thyratron, a condenser'which is--charged-whilethe timer contacts are separated-and isdischarged: while the contacts are engaged, acmmectiQn-between the condenser "discharge circuit andthe thyratron grid'such that the-grid is positively biased and the thyratron isionized during the period of contact closure, a circuit which includes in series the plate of the oscillator tube, the cathode of the oscillator tubeandthe-plate of the thyratron bothat ground or zero potential and the cathode of the thyratron and means for intermittentlyimpressing positive potential on the plate of the'oscillator tube while the cathodeof the thyratron" is negative with respect to ground whereby pulses 01" current flow through the oscillator tube-.- In oneform of -the-invention, the means is a' source of alternating current of high frequency. Inanother formthe means is a second condenserwhich .dischargesintermittently at highfrequency, saidsecond-condenser being charged through a resistance inseries therewith, the R. C. relation'ofrthe second condenser and seriesresistan'cebeing such that frequency of charge and.di-scharge of the second condenser is relatively-high.

Further objects and-advantages of th r resent invention will :be-apparentfromthe following description, reference being had to the accompanying drawings, whereinpreferredv embodiments ofthe present invention are clearly. shown.

In the drawing:

Fig. 1 is a wiring diagram of 'a-n-embodiment of the present invention.

Fig. 2 shows a modification of F the diagram of Fig. 1.

Referring tol ig;v 1, a-transformer. primarylll is connected with an alternatingicurrentsource SI of high frequency. F01". an engine-operating at 2500 R. P. M., the-frequency of the-source SI should be at least3750 cycles persec'ond' in order to obtain 4% accuracyof timing; This frequency could be generated by-a l high :poweraudio oscillatoror by a rotary-machine: Secondary. wind= ingsv ll, 22 anda23 are:associated;with;the primary winding-Ii lllr.v Asrectifier: tube 520 1 has'zitsi; cathode :2 l connected ivithzthemnding ;2 ziandzits plates l3 and I!) connected respectively with terminall2 and tap 14 of the winding I I. The tap i3 is connected with a terminal C. The cathode 2! is connected with a terminal B. The condenser 35 is connected with the terminals B and C. Terminal N5 of secondary l I is connect'ed'by wire it with a terminal A.

Terminal B is connected with-terminal D of a timer T driven by the engine. The timer comprises a support 26 connected with timer terminal D and connected by a leaf spring conductor. 2'! with a circuit breaker lever 28 pivoted at 29 and carrying a rubbing block or'cam follower 1H. for engaging a cam SZrotated by an engine driven shaft 30. Lever 28 carries a contact 33 for engaging a contact at. A resistance 36; preferably 3000 ohms, is connected between the contact3t and a terminal E. A resistance 37, preferably 30,000 ohms, is connected between terminal E and terminal C.

A thyratron tube has a plate 54 connected with wire 38, a grid 39 connected with terminal E, a cathode M connected with terminal'C and a cathode heater 4?. connected with a groundedrm sistance 43 and with wire 25 connected with wire 38 and with wire 2 2 connectedwith secondary winding 23.

An oscillator tube 45 has a cathode Mi which is grounded and which is connected with wire-38 and which is in parallel with a condenser tea. Tube 45 has a plate il connected with wire 48; connected with choke 49- connected by'wire I! with terminal A. Tube 45 has a grid 50 connected by wire 5! with a resistance 52 in parallel with a condenser 53, both together'being connected with one end of the primary 55 of an oscillator coil 54, the other end of which is connected by wire 5'! with a condenser 58 connected with-wire 58. An adjustable condenser is connected across the terminals of the primary 55 of the coil 54. The primary 55 is divided into two sections 55a and 55b by a tap 55c which is grounded;

The oscillator coil 5d has a secondary til-com nected selectively by distributor MD with priquencies of the resonators can be adjusted" by" endwise movements of I magnetizable-rods 8'! sur denser 35 discharges through these contacts and resistances 36 and 3! which retard discharge so that thyratron grid 39 will be positively biased and the thyratron will be ionized as long as possible during the period of .contact closure. During the period of ionization of thyratron 40, it is in condition to pass current from its plate 44 which is at ground potential to its cathode C when the latter is at negative potential with re- 1 spect to ground. Terminals or points A and C are connected with the points I and I3 of the transformer secondary II which is inductively connected with an A. C. source of relatively high frequency. When A is positive, C is negative, and vice versa. During half of the A. C. wave when C is negative and A is positive, current will pass through the following circuit: terminal A, wire I'I, choke 49, wire 4'18, grid ll of oscillator tube 45, cathode 36 of tube 45 and plate 40 of tube 40 (both at ground or zero potential) cathode II and terminal C. When C is positive and A is negative no current will pass through this circuit. Therefore the oscillator is intermittently operative and sparks will occur at a plug at the frequency of the A. C. source connected with transformer primary I0.

Instead of using a power supply or power pack requiring high frequency input for obtaining high frequency plate supply, the same effect can be; obtained by the use of an R. C. circuit in the power pack where the time constant of R. C. is

the required value, for example, 250 (ohms,-resistance) X 1 (microfarad, capacity),the equiva:

lent of 4000 cycles per second alternating current plate supply.

Fig. 2 shows the modification of Fig. 1 in order to use an R. C. circuit. The source 52 connected;

to the transformer primary 90 may be at the usual frequency. The transformer secondary 23 is connected as in Fig. 1. The transformer secondary 9| has end terminals 92 and 94 and a center tap 93. The secondary winding 95 is connected with the cathode filaments 96 and 91 of rectifier tubes I00 and IIII having their plates 08 and 99, respectively, connected with terminals 92 and 90, respectively. Terminal 93 is connected with wire I03, connected with terminal C. Wire I05 connects the cathode filaments 96 and 91 with a choke I00, connected by wire I08 with terminal B. Filter condenser I0? is connected between the wires I05 and I03. Filter condenser I 09 and a parallel resistance iii? are connected between wires I03 and I03. A resistance III, preferably 250 ohms, is connected between terminals B and A. A condenser I I2, preferably one microfarad, is connected between terminals C.

4 cording to Fig. 2 is as follows. While contacts 33, 34 are open condensers I09 and H2 are charged, wire I08 being positive and wire H0 neg ative, Terminal A is connected with the positive terminal of condenser I I2 and terminal C with its negative terminal. During engagement of contacts 33, 34, condenser I09 discharges through resistance H3, contacts 33 and 34 and resistance H4. These resistances retard discharge of condenser I09 so that thyratron grid 39 will remain positively biased and thyratron Ml will remain ionized as long as possible during the period of contact closure. When the thyratron is ionized, condenser IIZ discharges through the circuit A to C described with reference to Fi 1 and the oscillator becomes operative. When the potential of the terminal A falls so low that current flow from A to C ceases, the condenser I I2 is recharged until the potential of A is such that current flow from A to C is resumed. Therefore current flows from A to C intermittently at the rate determined by the R. C. relation of resistance III and condenser II2. If resistance of III is 250 ohms'and the capacity of H2 is one microfarad, the timer constant of the combination (resistance III and condenser I I2) is 250x 1x 10- which is the equivalent of 4000 cycles per second. The discharging of the condenser I I2 can take place because, concurrently, the plate 41 of tube 45 is more positive than ground (potential of its cathode t0 and of plate 44 of thyratron while potential of C is more negative than ground.

The operation of the oscillator is the same in both circuits. Whenever a sufiicient voltage is impressed on the plate A? of tube 55, the oscillator tube 45 permits current to fiow to charge the condenser 85. The condenser charging circult includes secondary terminal I5, wires It and I I, choke :30, condenser 58, condenser 85, resistance 52, wire 5|, grid 50, cathode 46, wire 38, plate 44, cathode ii, wire 2|, terminal C and secondary tap I3. During the charge of condenser 85, the voltage impressed on the grid becomes increasingly positive. As grid 50 becomes more positive, tube 45 passes more current and the voltage drop across the tube decreases. As the voltage drop decreases across tube 45, the condenser 85 starts discharging and produces a negative voltage on the grid 50 due to the operation of two inductively related circuits. One of these circuits is condenser 85, wire 51, all of the oscillator primary coil 55. The other circuit includes the grounded tap 550 of primary '55, the primary section a, resistance 52, wire -5I,

' grid 50,,cathode 46 and ground connection back to 550. The negative voltage impressed on grid 50 causes less current to fiow from the plate 41, thereby raising the voltage drop across the tube t5 and allowing the condenser to be charged again. In this way, an oscillation through the primary 55 is sustained. This oscillation increases rap-idly in amplitude until the maximum amplitude is reached; and the oscillation is sustained so long as sufiicient voltage is impressed on the plate 41 of oscillator tube 45. In other words, the oscillator tube 45 operates in a manner analogous to a variable resistance in shunt with the condenser 85. As condenser charge in creases the variable resistance decreases auto matically; and, when the decrease of resistance is such that the condenser is robbed of charging current, the condenser discharges. The discharge of-the condenser automatically causes thevariableresistance to increase whereby the condenser is permittedto receive a charging current: and

the cycle is repeated so long as suflicient voltage is being impressed on the plate 47 of tube 45.

As the current oscillation through the oscillator primary coil 55 increases in magnitude, the resonator then connected with the oscillator by the distributor 60D while the timer contacts are closed, will have, in its condenser-coil circuit, a corresponding oscillation increasing in magnitude until voltage impressed upon the spark plug is sufficient to cause the current to jump the gap. Because positive potential is being intermittently impressed on terminal A while the potential of C is negative with respect to ground during the period of contact closure, the oscillator operates intermittently through the resonator then connected by distributor 66D to produce a shower of sparks at the plug connected with the resonator.

From the foregoing description of two embodiments thereof, it is apparent that the present invention resides in the combination with a resonator connected with a spark plug of an oscillator inductively associated therewith having a tube, a series circuit which includes a terminal A, the plate of the oscillator tube, the cathode of the oscillator tube and the plate of a thyratron both at ground 01' zero potential, the cathode of the thyratron and a terminal C, means con trolled by the engine timer for effecting ioniza tion of the thyratron during the sparking period, and means for intermittently impressing upon terminal A a positive potential while the potential of the terminal C is more negative than ground.

While the embodiments of the present invention as herein disclosed, constitute preferred forms, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. An ignition system comprising a spark plug, a resonator connected with the plug, an oscillator inductively connected with the resonator and having a tube including a plate and a cathode, a thyratron having a plate, grid and cath" ode, an engine operated timer having contacts, a condenser, a D. C. source for charging the con denser, a circuit including the condenser and the timer contacts, when closed, for efiecting condenser discharge and including resistances for retarding condenser discharge, a connection be tween the condenser discharge circuit and the grid of the thyratron such that the grid is posi tively biased and the thyratron is ionized during the period of contact closure, a circuit including in series a first terminal, the plate of the oscillator tube, the cathode of the oscillator tube and the plate of the thyratron at ground or zero potential, the cathode of the thyratron and a second terminal at the same potential, and means for intermittently impressing on the first terminal a positive potential while the potential of second terminal is negative with respect to ground, whereby current passes through said circuit intermittently to effect through the oscillator and resonator a rapid succession of sparks at the plug during the contact closing period.

2. An ignition system according to claim 1 in which the first and second terminals are connected with an A. C. source of relatively high frequency.

3. An ignition system according to claim 1 in which the first and second terminals are respectively connected with the positive and negative terminals of a second condenser which is charged by the D. C. source, and in which the charging circuit of the second condenser includes a resistance in series with the second condenser, the time constant of the second condenser and series resistance being such that the condenser discharges and recharges at relatively high frequency duringjhe period of contact closure.

4. En ignition system comprising a spark plug, a resonator connected with the plug, an oscillator inductively connected with the resonator and having a tube including a plate and a cathode, a thyratron having a plate, grid and cathode, an engine operated timer, means under control by the timer for effecting ionization of the thyratron during the period required for ignition, a circuit including in series a first terminal, the plate of the oscillator tube, the cathode of the oscillator tube and the plate of the thyratron at ground or zero potential, the cathode of the thyratron and a second terminal at the same potential, and means for intermittently impressing on the first terminal a positive potential while the potential of the second terminal is negative with respect to ground, whereby current passes through said circuit intermittently to '1; through the oscillator and resonator a rapid succession of sparks at the plug during the contact Closing period.

BROOKS H. SHORT.

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

UNITED STATES PATENTS Number Name Date 1,334,095 Hill Mar. 16, 1920 2,169,818 Scott Aug. 15, 1939 2,338,906 Dausinger Jan. 11, 1944 2,347,286 Sandretto Apr. 25, 1944

Images