US3450940A - Electrical pulse generating apparatus - Google Patents

Description

June 17, 1969 I. E. LINKROUM 3,450,940

ELECTRICAL PULSE GENERATING APPARATUS Filed Aug. 29, 1967 N 117 C m m RECTIFIER INVENTOR. IRVING E. LINKROUM 5; mmfzf nm ATTOR EYS 3,450,940 ELECTRICAL PULSE GENERATING APPARATUS Irving E. Linkrourn, Hancock, N.Y., assignor to The Bendix Corporation, a corporation of Delaware Filed Aug. 29, 1967, Ser. No. 664,171 Int. Cl. H05b 41/00 US. Cl. 315-171 Claims ABSTRACT OF THE DISCLOSURE This invention relates to electrical apparatus and more particularly to electrical pulse generating systems, such as ignition spark generating systems for combustion engines and the like.

One of the objects of the present invention is to provide novel electrical circuitry for generating simultaneous spark discharges at two series connected spark gaps.

Another object is to provide a novel combination of high and low energy pulse generating circuits for alternatively firing a common ignition gap.

A further object is to provide a simplified, highly efficient ignition system which is novelly so constructed as to increase the normal operating life of the components which are most likely to fail.

Still another object is to provide a spark generating system for combustion engines comprising a novel series dual high energy starting circuit in novel combination with a lower energy continuous duty circuit.

The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawing. It is to be expressly understood, however, that the drawing is for the purpose of illustration only and is not intended as a definition of the limits of the invention.

In the drawing, the single figure is a schematic diagram of one form of electrical circuit embodying the invention.

The single embodiment of the invention illustrated in the drawing by way of example is in the form of an untimed ignition system for jet or gas turbine type engines. In these engines one level of spark energy is required to be supplied, preferably to a pair of ignition plugs, for starting the engine, but a lower level of spark energy is adequate to enable one igniter plug to perform its functions as required when continuous operation of the engine is desired. This mode of operation of the ignition system results in a longer operating life for the igniter plugs and other components of the system. The illustrated system accordingly comprises a first starting circuit 5 for supplying relatively high energy, say 2 joules or more, at each of two series connected igniter gaps and a second continuous duty circuit 6 novelly associated with the first circuit for supplying a lower energy, say 0.5 joule, to one of the igniter gaps. These circuits may be alternatively energized at the option of an operator or pilot by any suitable source of alternating or interrupted direct current, such as by a 115 volt 400 cycle A.C. generator.

In the high energy circuit 5 when switch 7 is closed, a

nited States Patent 0 relatively large storage capacitor 8 is connected to be charged, step by step, to some preselected voltage, say 2,000 volts, through a transformer 9 and a suitable rectifier 10 in a known manner. A small storage and triggering capacitor 11 is connected across capacitor 8 in series with a resistor 12 and the primary winding 14 of a high frequency transformer 13 through leads 15 and 16. Capacitor 11 will accordingly be charged at the same time and to the same voltage as capacitor 8. When switch 7 is open and switch 17 is closed, a storage capacitor 18, which is smaller than capacitor 8, is connected to be charged in a similar fashion through a transformer 19 and a rectifier 20 to a preselected voltage, say 2500 volts. These capacitors when thus charged constitute sources of pulse energy to be supplied to a pair of igniter gaps or plugs 21 and 22 which may be of the so-called low tension shunted-surface gap type.

When the high energy circuit is in operation for energizing both igniter plugs 21 and 22 for starting the engine, the discharging of capacitor 8 is in part controlled or triggered by a sealed control gap 23 having a predetermined spark-over or on-set voltage of say 2000 volts. Gap 23 is connected across capacitor 8 in series with a small capacitor 24 and a primary winding 25 of a high frequency transformer 26 through leads 27, 28 and 16. Whenever the charge on capacitor 8 reaches the spark-over voltage of control gap 23, it will discharge a small part of its charge across the gap through primary winding 25 into the small condenser 24. This discharge pulse will induce a high voltage pulse in the secondary winding 29 of transformer 26 which is connected at one end to the ungrounded terminal of igniter gap 22 and at its other end to the low voltage terminal of capacitor 8. The voltage is stepped up sufiiciently by transformers 25, 29 to ionize igniter gap 22. The ionizing circuit is completed through ground and a small capacitor 30 which may be the inherent capacitance of the line or circuit components to ground.

Similarly and at the same time, upon breakdown or conduction of control gap 23, as explained above, capacitor 11 will discharge through said gapacross primary winding 14 to thereby induce a high voltage pulse in secondary winding 31 of high frequency step-up transformer 13. One end of winding 31 is connected to the un grounded terminal of igniter gap 21. The other end of winding 31 is connected to the high potential terminal of capacitor 8 through a control gap 32 having a spark-over voltage, say 4000 volts, considerably in excess of the spark-over voltage of control gap 23. The induced voltage in winding 31 is of sufficient magnitude to bridge gap 32 and ionize igniter gap 21. The bridging and ionizing circuit is completed through ground and a small capacitor 33 which may be the inherent capacitance of the line or circuit components to ground. To better insure the breakdown of gap 32 by the short low energy pulse in secondary winding 31, it is desirable to mount gaps 23 and 32 in a manner such that light from gap 23 when it fires will fall upon gap 32 and speed up the breakdown thereof.

With control gap 32 conductive and both igniter gaps 21 and 22 ionized in the manner described above, high energy storage condenser 8 will discharge across and produce high energy sparks at the igniter gaps via lead 27, gap 32, secondary windings 31 and 29, and lead 16. In the event igniter plugs 21 fails to conduct for any reason, the discharge of condenser 8 proceeds via an inductor 34 and ground to igniter plug 22. If, on the other hand, plug 22 fails to conduct, the condenser discharge will proceed from igniter plug 21 via ground and an inductor 35 to lead 16. The parameters of the circuit components are such that inductors 34 and 35 will delay appreciable conduction therethrough until igniter gaps 21 and 22, respec- 3 tively, break down if the latter are functioning properly.

Once the engine is started by high energy sparks resulting from the discharge of capacitor 8 in the above manner, switch 7 is opened to de-energize the high energy circuit and switch 17 is closed to energize the continuous duty low energy circuit 6 wherein the discharging of storage condenser 18 is controlled by a sealed gap 36 having a preselected breakdown or on-set voltage, say 2500 volts, somewhat in excess of the breakdown voltage of gap 23. One terminal of gap 36 is connected to the high potential side of capacitor 18, and the output terminal thereof is connected through a lead 37 to ground and hence, to the low potential terminal of capacitor 18 through parallel paths, one of which comprises a primary winding 38 of transformer 26, a resistor 39 and a small condenser 40 connected in series, and the other of which comprises secondary winding 29 of transformer 26 and igniter gap 22.

Whenever the charge on capacitor 18 attains the breakdown voltage of control gap 36, the latter is rendered conductive, and there results an initial discharge of the capacitor through primary winding 38 and resistance 39 to capacitor 40. This pulse induces a high voltage pulse in secondary winding 29 which is effective to ionize igniter gap 22 and render the same conductive to the discharge of capacitor 18 and hence, create a relatively low energy spark in the engine combustion chamber. The resistance 39 clamps and shortens the condenser discharge pulse through primary winding 38 to thereby avoid sufficient build-up of voltage in primary winding to fire igniter plug 21 through transformer 13. The triggered spark gap arrangement in the high energy circuit 5 prevents the low energy circuit 6 from firing back into the high energy system through transformer 26.

The operations of the high and low energy circuits 5 and 6 as described above are repetitive and generate a succession of sparks at the igniter plugs. The sparking rate may be controlled by the circuit parameters and the magnitude of the source voltage. By way of example, in some engines the spark rate requirement may range from one to five sparks per second.

In one successful jet engine ignition system embodying the invention, wherein the source voltage varied from 100 to 125 volts and the breakdown or spark-over voltages of the control gaps were of the magnitudes suggested above, other basic components had the values indicated below:

Capacitor 8 7 microfarads. Capacitor 18 0.8 microfarad. Capacitors 11 and 24 0.2 microfarad. Capacitor 40 0.02 microfarad. Resistance 12 50K ohms. Resistance 39 5 ohms. Inductors 34 and 35 80 turns #19. Primary windings 14, 25 and 38 3 turns #17. Secondary windings 29 and 31 turns #17.

It will be noted that the on-set voltage (4000 v.) of gap 32 is sufficiently high to prevent any flow of energy through igniter plug 21 when the 2500 v. system 6 is in operation to fire plug 22. Additionally, the initial discharge of capacitor 18 through primary 38 into the small capacitor 40 is of high frequency and short duration and hence, the induced voltage in secondary 29 is incapable of triggering gap 32, as is also the induced voltage in primary 25. The latter is also insufiicient to charge capacitor 11 to the on-set voltage of gap 23. Similarly, such triggering of gap 32 cannot be effected by the subsequent 2500 v. discharge through winding 29 from capacitance 18. When the high energy circuit 5 is operating under control of the 2000 v. gap 23 the voltage induced in winding 38 is less than 2000 v. and hence, insufficient to fire across the 2500 v. gap 36. In addition to the foregoing advantages which result in part from the use of a triggering gap system in the high energy circuit, the oper- 4 ating life of gap 32 which carries the high energy discharge of capacitor 8 is materially enhanced by the fact that the repetitive breakdown thereof is effected by lowenergy, high-voltage pulses from transformer 13.

Although only a single embodiment of the invention has been illustrated in the drawing and described in the foregoing specification, it will be understood that the same is not thus limited. For example, high tension igniter plugs could be used in lieu of the low voltage plugs illustrated and inductors 35 and 36 could be replaced by suitable gaps. Various other changes, particularly in the exemplary component values suggested and in the arrangement of components illustrated may also be made without departing from the spirit and scope of the invention as the same will now be understood by those skilled in the art.

What is claimed is:

1. An electrical pulse generating system comprising a first storage capacitor, a second storage capacitor, means for simultaneously charging said capacitors to a predetermined voltage, a step-up transformer comprising a primary and secondary windings, first control means for initiating the discharge of said second capacitor through said primary winding, a load circuit connected across said first storage capacitor and comprising said secondary winding and second control means responsive to the voltage induced in said secondary winding for initiating discharge of said first capacitor through said load circuit.

2. An electrical pulse generating system as defined in claim 1 wherein said capacitors are connected in parallel circuits to a common source of electrical energy.

3. An electrical pulse generating system as defined in claim 2 wherein said source charges the capacitors stepby-step to the predetermined voltage.

4. An electrical pulse generating system as defined in claim 1 wherein said first control means is a triggering gap having a flash-over voltage substantially equal to said predetermined voltage.

5. An electrical pulse generating system as defined in claim 4 wherein said second control means is a control gap having a flash-over voltage in excess of the flash-over voltage of said triggering gap.

6. An electrical pulse generating system as defined in claim 1 wherein said load circuit includes an igniter plug.

7. An electrical pulse generating system as defined in claim 6 comprising a second transformer having primary and secondary windings, a third capacitor connected in series with said last-named primary winding and said first control means across said first capacitor, and a second igniter plug, the latter and the secondary winding ofsaid second transformer being connected in series with said first-named igniter plug and said second control means in said load circuit.

8. Electrical spark generating apparatus comprising a first storage capacitor, a voltage step-up transformer having primary and secondary windings, a second storage capacitor connected in series with said primary winding across said first capacitor, a triggering gap having a predetermined breakdown voltage connected in shunt across said primary winding and said second capacitor, a load circuit comprising an igniter gap, a control gap connected in series with said secondary winding across said first capacitor, said control gap having a breakdown voltage in excess of said predetermined voltage, means for repetitively charging said capacitors simultaneously to said predetermined voltage, whereby said triggering gap is rendered conductive to the discharge of said second capacitor through said primary winding to thereby induce a sufiicient voltage across said secondary winding to render said control gap and igniter gap conductive to the discharge of said first capacitor.

9. Electrical spark generating apparatus as defined in claim 8 comprising a resistor connected in series with said second capacitor and said primary winding.

10. Electrical spark generating apparatus as defined in claim 8 comprising a second transformer having primary and secondary windings, a third capacitor connected in series with said primary winding of the second transformer and said triggering gap across said first capacitor, and a second igniter gap and said secondary winding of the second transformer connected in series with said first-named igniter gap and said control gap in said load circuit.

11. Electrical spark generating apparatus as defined in claim 10 comprising an inductor connected in shunt with a portion of the load circuit including said firstnamed igniter gap.

12. Electrical spark generating apparatus as defined in claim 11 comprising an inductor connected in shunt with a portion of said load circuit including said second igniter gap.

13. Electrical spark generating apparatus as defined in claim 10 comprising a fourth capacitor, a second control gap having a breakdown voltage below that of said first-named control gap and above that of said triggering gap, means for repetitively charging said fourth capacitor to the breakdown voltage of said second control gap, a second primary winding inductively coupled with the secondary winding of said second transformer and a fifth capacitor, said second control gap, said second primary winding and said fifth capacitor being connected in series across said fourth capacitor and said second control gap, said secondary winding of the second transformer and said second igniter gap being connected in series across said fourth capacitor.

14. Electrical spark generating apparatus as defined in claim 13 comprising a resistor connected in series with said fifth capacitor.

15. Electrical spark generating apparatus as defined in claim 13 comprising means for selectively connecting said first capacitor and said fourth capacitor to their respective charging means.

References Cited UNITED STATES PATENTS 3/1964 Collins 3l5209 X 6/1967 Segall et al. 315-209 JOHN W. HUCKERT, Primary Examiner. R. F. POLISSACK, Assistant Examiner.

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