US2551101A - Electrical ignition system - Google Patents

Description

y 1,1951 7 w. R. DEBENHAM ET AL ELECTRICAL IGNITION SYSTEM Filed March 9, 1949 in van fors WMAQ MM 2 B Attorneys Patented May 1, 1951 ELECTRICAL IGNITION SYSTEM William-Richard Debenham and John Clifford Shenton, Farnborough, England Application March 9, 1949, Serial No. 80,514

' In Great Britain March 10, 1948 31 Claims. (01. 315- 209) place at the latter for each operation of the contact breaker at the low frequency source.

, High intensity ignition apparatus for use where precise timing, as for a piston engine, is unnecessary, is also known in which a charge accumulating condenser is connected to receive via a relatively high voltage charging spark gap repeated unidirectional charges from an induction coil and to discharge via a realtively low voltage discharging spark gap when the voltage of the accumulated charge thereon reaches a predetermined value to supply energy to a spark plug.

The present invention has for an object to provide improvements in such high intensity ignition apparatus for use, for example, ,for turbine or jet type engine ignition, cabin heaters, flame warfare apparatus and fog disposal ap aratus, apparatus in accordance with the invention having been evolved in the first place for use for starting and restarting turbine or jet type aircraft engines at any altitude.

According to the invention, in high intensity ignition apparatus in which a charge accumulating condenser. is connected to receive via a relatively high voltage charging spark gap repeated unidirectional charges from an induction coil and to discharge, when the voltage of the accumulated charge thereon is suificiently high, via a relatively low voltage discharging spark gap and a spark plug lead, means are provided to reduce the interelectrode voltage of said gap,.and ensure its rapid extinction or suppression, each time the induction coil voltage declines and/or changes polarity and thus prevent or reduce the oppormeanscomprise a small auxiliary condenser connected via series resistance across the induction coil connections at that side of the charging gap remote from the charge accumulating condenser. The values of such auxiliarycondenser and its series resistance are not critical for any particular induction coil and are so chosen that they have the efiect that extinction of the charging gap is ensured each time the induction coil voltage declines and then changes polarity and that the value of the changed polarity voltage is re duced so that no appreciable reverse voltageis developed across the charging gap at anytime adding to the voltage across the charge accumulating condenser, whereby opportunity for discharge of the charge accumulating condenser reversely through the charging gap is reduced.

The provision of such interelectrode voltage reducing means according to the invention enables the use, for a given maximum charge voltage of the charge accumulating condenser, of a charging gap of substantially lower break down voltage and an induction coil of correspondingly lower output voltage than would otherwise be possible, and thus substantially increases the efficiency of the apparatus. v

According to a feature of the invention there is connected in series with the charge accumulating condenser in the charging and discharging circuits thereof a small inductance across which, each time the charging gap breaks down, a tramsient high frequency voltage is developed, by the transient high frequency current which then flows in the charging circuit due to the self-capacity of the induction coil and any added shunt capacity, which reduces the accumulated charge voltage required to break down the discharging spark gap by the efiective amount of the transient high frequency voltage and reduces pre-breakdown corona and brush discharge losses in said gap. I

The transient high frequency voltage developed in this way will depend on thecharacteristics of the series inductance employed and also on the self-capacity of the induction coil and any added capacity, but preferably, series resistance, which may be variable, is provided in the'chargingcircuit of the charge accumulating. condenser to control the transient high frequency voltage as required. 1 Being in series in the discharging circuit of the charge accumulating condenser, this 7 small series inductance, besides effectively reducing the accumulated charge voltage required to break down the discharging gap, has the efiect of limiting the peak discharg current through the discharging gap and also acts, in conjunction with capacity associated with the spark plug lead, to increase the voltage produced at a plug with which the latter is connected.

In order to obtain a high ratio of output energy, i. e. spark plug discharge energy to input energy, to minimise the value of the high voltages developed and to prolong the useful life of the spark plugs used with highintensity ignition apparatus according;- to: the invention, it is preferable that the latter should be of low voltage type in which the discharge takes place over the surface of the insulation between electrodes which are preferably of substantial size to minimisethe effects of erosion of the material thereof. The, break down voltage of such a plug under normal ground level conditions may, for example, be of the same order as that of the discharging gap;. It 1828.180

desirable from the point of view of minimising high voltage values that the spark plug lead should have such leakage. or insulation resistance as will, by being in shunt across a spark plusubstantially reduce the voltage required to break down, or initiate'a discharge in, the discharging gap; Such shunt resistance may be comprised as to a substantial proportion thereof by aresistor provided for 'the purpose, but where'a low voltage spark" plug of the type referred to is employed, this may present a semi-conductive discharge path. Thus a deposit applied to, and/or formed during menu, the insulating material overwhich the discharge takes placecan alford some orall of the desirable leakage resistance. W here mica is used as" theinsulating material, colloidal graphite maybe burned, as by an applied. flame, on to the mica surface before the plug is connected' for use. to protect the apparatus, for example, should it be operated with no-spark plug.

In" some cases, however, for example, when it is required to employ conventional high voltage type spark plugs of which the break down voltage under normal ground level conditions may be several times that ofthe discharging gap, a considerably higher voltage is required to initiate a discharge at a spark plug than is required to maintain" such discharge, but such high discharge-initiating voltage may; in general be of very'brief duration compared with the duration of the discharge as a whole so that the greater partof the energy transmitted to a spark plug may be at'the lower voltage which need be only just suflicient to maintain the discharge.

The auxiliary or suppressor condenser employed as above set forth to ensure rapid extinction ofthe-charging gap may be utilised, with or without a smallseries inductance as above set forth, for providing a high discharge-initiatingvoltage, and according to a further feature of the invention the auxiliary or suppressor condenser is connected to supply energy to the spark plug-lead via a third spark gap, whereby the discharge at a spark plug is initiated at relatively high voltage by energy from thesmall suppressor condenser, to be maintained by energy from the charge accumulating condenser at a lower voltage corresponding to that required to break down the'discharging gap when there is already a discharge at the plug. Some series inductance in the discharging circuit is, however, desirable if onlyjto limit'the peak value of the discharge through thedischarging gap;

A resistor is, however, desirable In such a case, particularly when a surface discharge plug as above set forth is used, energy may be fed from the auxiliary or suppressor con denser via the third gap directly to the spark plug lead. Alternatively, however, particularly when a conventional high voltage plug is used, a third spark gap of which the break down voltage is not substantially less than that of the charging gap may be connected in series with the primary winding of a high frequency transformer across the auxiliary condenser, the secondary winding of the transformer being connected in series with the discharging gap between the-latter and the charge accumulating condenser, so that when the voltage of the charge on the auxiliary condenser becomes instantaneously high enough the third spark gap. breaks down and the resulting high frequency voltage induced in the transformer secondary winding is eifectively added to the voltage of'the charge on the charge accumulating condenser.

Figures l', 2, 3 and 4 of the accompanying drawings. are circuit diagrams showing compomerits and connection of four typical high intensity ignition arrangements according to the onlyof' this coil is shown in Figures 2, 3 and l,

the primary winding being shown at l2; the vibrating reed at i3, contact shunting condenserat It, an exciting battery at lt'and a manual onoffswitch at l6 on1y in Figure 1. In each case, the self capacity of. the secondary winding l l is indicated by broken lines we condenser ll, in put leads at i la; a relatively high voltage charging'spark gap at 18,2. charge accumulating'condenser at I9, a relatively low voltage'di'scharging spark gap at 20, a spark plug lead at 2911, a spark plug at 2!, shunt resistance and capacity associated with the plug lead 20a at 22" and 23, respectively, an auxiliary condenser and series resistance connected across the induction'coil H atv 24 and 25, respectively, and a resistance connected in series in the charging circuit of the charge accumulating condenser l9 at 26, whilst in Figure 1, a' small inductance connectedin series in bethsaid charging circuit and in the discharging. circuit of the condenser [9 is indicated at 2?. Both the spark gaps l3 and'Zll are of knownenclosed and sealed type for aircraft use, the charging gap lBat least preferably comprising electrodes composed of sintered nickel and alumina enclosed'in hydrogen gas;

The. arrangement of- Figure 1 isintended for use with a low voltage spark plug 2| of a type comprising substantial-inner and outer electrodes, which by virtue of their size are more resistant to the effects of erosion than the wire-like electrodes of conventional high voltage type plugs, which define between them an annular space filled with insulating material presenting an annular surface, substantially flush with the ends of the electrodes, over which surface the discharge occurs, the voltage required to' initiate a discharge across this plug when operating, with a carbon deposit bridging the annular insulation surface, under normal ground level conditions, being of the order of two kilovolts or less. It

is found that where the insulating material of such a plug is mica and is tightly compressed between the inner and. outer electrodes and Where there is a'deposit of carbon over the annular mica surface, the mica becomes eroded in use to a less extent than the metal of the electrode so that the plug has a long useful life.

The relatively high voltage charging gap I8 is such as to break down when the voltage'across it is two or more times the voltage required to break down the discharging gap 28 and the break.

downvoltage of the latter is of the same order as that required to initiate a discharge at the plug 2| under normal operating conditions. It will be observed that the effective or charging impulses induced in the coil H are all of the same polarity corresponding to the breaking of the vibrator contacts and that the intervening impulses corresponding to making of said contacts are of opposite polarity and at a much lower voltage. The voltage of each effective or charging impulse is applied across the charging gap It by way of the charge accumulating condenser I9 and the small series inductance 27.

Each time the voltage across the charging gap I8 reaches a given value dependent upon the virtually a short-circuit at the high frequencies involved but the characteristics of the small series inductance 2'! are such that the latter offers substantial impedance at said high frequencies, andthus, during the brief duration of each discharge of the self-capacity I'I, there is developed across the inductance 2! a transient voltage which is effectively added to the voltage of the accumulated charge of the condenser I9.

The voltage developed across the series connected inductance El and the charge accumulating condenser I9 is applied, via the shunt resistance and condenser 22 and 23 and the spark plug 2i, across the discharging gap 20, but only when the accumulated charge voltage of the condenser I9 has been built-up (as a resultof a series of successive charging impulses from the coil If, each breaking down the charging gap I8 and adding its quota to the charge of the condenser) to a value which plus the effectively added transient high frequency voltage developed (each time the charging gap I8 is brokendown) across the small series inductance 21, reaches a sufficiently high value, will the discharging gap break down, whereupon the charge accumulating condenser I9 discharges via the discharge gap 20 and the spark plug 2|. The resistance 22 effectively shunts the spark plug 2i and thus reduces the maximum voltage required to a value much nearer the break down voltage of the discharge gap 20 than to the arithmetical sum of the break down voltages of said gap 29 and of the plug 2|.

Although it is desirable for reasons of safety, e. g. in case the apparatus shouldbe operated without a spark plug connected, that the resistance 22 should be comprised, in part at least,,by an actual resistor connected as shown, thisre sistance can be comprised by a semi-conductive surface or discharge path between thespark plug electrodes. The plug illustratedbyfFigure 5 of the'draw'i'ngs has a"substantial solid cylindrical central electrode 5I'between which and a substantial hollow cylindrical outer'electrode 52 is compressed tightly an annular insulating body 53 of mica, the end faces of-said' electrodes 5| and 52 and of the mica insulating body 53 being'substantially flush with one another. With such a spark plug the semi-conductive surface or discharge path can be comprised by a deposit applied-to, or formed during operation, upon the end face of the mica insulating body 53 as indicated at 54. Such a deposit may be formed by burning colloidal graphite, as by an applied flame, on to the end surface of the mica insulating body 53. Y

The amount of transient high frequency current which flows in the inductance 21 each time the charging gap is breaks down is dependent on. the characteristics of said inductance 21 and on thevalue of the self-capacity if, and addi- 'will decline and may even, due to the subsequent make operation of the reed I3, change polarity 1 before the charging gap #8 is extinguished, and before the charge period of the charge-discharge cycle of-the condenser I9 is complete, and that the reverse voltage so produced across the charg-- ing gap It may be sufficient to maintain the-latter broken down (i. e. conductive) and allow substantial discharge of the condenser I9 to take place r'eversely through the charging gap I8. The values of the auxiliary/"condenser and its series resistance 25 connected across the coil II, which are not critical in any particular case, are such, however, that the voltage at the coil side or electrode of the charging gap I3 will be maintained long enough after each effective impulse from the coil I I to ensure the rapid extinction of the'gap' It as the coil voltage declines and then changes polarity and that the opposite polarity makef voltage of the coil I I will be decreased so that said gap I3 will not have any appreciable voltage developed across it at any time adding to the voltage across the charge accumulating condenser, and thus opportunity for discharge of the charge accumulating condenser reversely through the charging gap i8 is greatly reduced or eliminated.

Although the efficiency of the arrangement of Figure l is increasedby the transient high frequency voltage developed across the small series inductance 21 due to the prevention or reduction thereby of corona and/or brush discharge in the gap 20, this inductance is not essential and may be omitted. In that case, however, the inclusion of'a small series inductance inthe discharging circuit alone is desirable, if only to limit the peak value of the discharge current, and so protect the discharging gap 20. A series inductance in the discharging circuit alone will act in conjunction with the capacity 23 associated with the spark plug lead to augment the voltage developed at the plug 2I. An appropriate small series inductance at 21, however, is clearly preferable because in this position it will serve all three purposes;

ass 1,101

TheiarrangementiofFigure 1 will operate satisfactorily with relatively large values of capacity at 23 so. that it is quite practicable to .include a switch in the plug lead so that "a single arrangement may be used, for example, for starting or restarting a number of engines in succession, the capacity at 23 being dependent upon the lengths of the leads andupon the switch emplayed.

"The arrangement of Figure 2 is intended for use where it is desired that each discharge at the ,plug should be initiated at high voltage and then maintained by energy at a lower voltage from the charge accumulating condenser l9. As transient high frequency voltages superimposed upon the charge voltage of the charge accumulating condenser l9 are not now required the small inductance 2'! is omitted and two small series inductances 21a and 21b in the discharging circuit alone are employed. Otherwise the arrange- .ment is the same'as thatof Figure 1 except that a third spark gap 30 is connected between the junction of the auxiliary condenser 24 with'the series resistance 25 and the junction of the two small inductances 21a. and 21b. The break down voltage of this thirdgap 30 is of the same order 2 'as that of the charging gap l8 and the latter and also the break down voltage of the-gap may be of the same order as in Figure 1. In operation, the voltage of the charge on the auxiliary condenser 26 reaches a value high enough to break down the third gap 30 before the voltage of the accumulated charge on-the condenser 19 is high enough to break down the discharging gap 29. The breaking down of the third *gap '3D--is accompanied by a discharge of energy from the auxiliary condenser .24 at the plug 2| and approximately at the same time the discharging gap 20 is also broken down, whereupon the discharge at the plug 2i is maintained by energy from the charge accumulating condenser 1-9 at the lower voltage than that at which said discharge is initiated by energy from the auxiliary condenser 24. The maximum voltage of the charge on the auxiliary condenser 24, and, therefore, the plug discharge-initiating voltage are dependent inter alia on the value of the series registor which is chosen appropriately in each particular case.

The arrangement of Figure 3 is also intended for use where it is desired that each plug discharge should be initiated at a higher voltage than the maximum voltage of the accumulated charge of the condenser Hi. In this case the third gap 39 has a similar or higher break down voltage than the charging gap I8 and is connected in series with the primary winding 3| of a step-up high frequency transformer across the auxiliary condenser 24, and the secondary winding 32 of the transformer is connected in the discharging circuit of the charge accumulating condenser 59 (e. g., as shown), between the .latter and the discharging gap 29. The secondary winding 32, incidentally, performs the same functions in the discharge circuit as-the inductances 21 of Figure 1, 21a of Figure 4, and 21a and 21b of Figure 2, which, as such, are omitted from-the Figure 3 arrangement. In operation, the third gap breaks down under the voltage of the charge on the auxiliary condenser 24 (which in this case is of somewhat greater capacity than in the case of Figure 1) before the voltage of th accumulated charge on the condenser 19 is .suflicient, of itself, tocause the discharging gap 20 to break down. The stepped up voltagecon- 'sequently induced in the high frequency transformer secondary winding 32 is applied to the discharging gap 20 and plug 2[ and breaks down both the latter and. the discharge therethrough isl'continued byenergy from the charge accumu- Jating .condenser 19 after the nergy from the auxiliary condenser 24 has been dissipated.

In both Figures 2 and 3 the third gap 30 is of known enclosed and sealed type, preferably like the charging gap l8.

Arrangements such as that of Figurez are intendedfor use with low voltage spark plugs and arrangements such as that of Figure 3 are intended for use with high voltage spark plugs, at 2|, but the arrangement of Figure 3 may be used for high or low voltage spark plugs.

It will be understood that the utilisation of the auxiliary condenser 24 to obtain a high plug discharge-initiating voltage, as in Figures 2 and 3, does-not appreciably, or at all, impair its operation to reduce the interelectrode voltage of the charging gap 18, provided that the capacity of the auxiliary condenser 24 is chosen appropriately in each particular case. The capacity of the condenser 24 will in all cases, be many times less than that of the charge accumulating condenser [9.

The arrangement of Figure 4 is a modification of Figure 1 in which the series resistance 25 via which the auxiliary condenser 24 is connected across the induction coil H is in series with the charging circuit of the charge accumulating condenser !9. For satisfactory operation the value of therresistance 25 of Figure 4 must be many times less-but the resistance 25 of Figure 4 must be :many times greater than in Figs. 1, 2 or 3. In view of the inclusion of relatively high resistance -at ZB-the'use of series inductance (such as 1'7, Fig- :ure 1-) to afiord transient high frequency voltages is not feasible and series inductance 21a as in Figure 2 is employed instead. Also the charge received by the charge accumulating condenser is at each effective impulse from the induction coil H- is reduced and an arrangement such as Figure 4 cannot, therefore, provide so many spark plug discharges, having the same energy, per second as arrangements such as Figure 1. Moreover, due to theabsence of an inductance as at 21 Figure 1, .pre-break down corona and brush discharges may occur across the discharging gap 20. Arrangements such asFigure 4 are intended for use Where highefliciency is not required.

Insall the arrangements shown a resistance 28 of which the Value is so high that it has negligible effect upon the performance is connected across the charge accumulating condenser [9 to ensure that "the latter becomes discharged when the apparatus is not in use. In some cases two or more coils II and corresponding charging gaps I8 may be connected in parallel to charge a single charge accumulating condenser l9.

Figural; when the booster coil vibrator operates :about'l500 times per minute.

'Gapacity of condenser 24 in Picofarads Resistor at 22, Kilohms n --Inductance 27 b in Microhenries inductance ratio of transformer 3l.32

Fig.

Inductance of coil 11 in Hcnries. Capacity 17 in 'Picofarads Breakdown potential of gap 18 in Kilovolts. Capacity of condenser 19 in Micr oiarads Break down potential of gap 20 in Kilovolts Resistance in Kilohms l 0L1: Resistance 26 in Kilohms Inductance 27 in Microhenri Permissible capacity at 23 in Picofara Maximum output, Kilovolts Break down potential of gap 30 in Kilovoltsu Inductance 27a in Microhenries Coupling of transformer 31.32

, Whilst a spark plug, such as that illustrated by Figure 5, having electrodes spaced by insulation presenting a semi-conductive discharge path between said electrodes, and especially one having a substantial electrodes between which mica insulation is tightly compressed and presents a treated surface, or a deposit thereon, a a semi- =conductive discharge path, is beneficial for use with or as part ofignition apparatus according to the invention, it has been found that such a plug is beneficial in other applications.

klt is, therefore, a feature of the invention to provide electrical ignition apparatus comprising a, condenser, such as [9, a charging circuit for connection with a source of charging voltage and from which dependent upon the voltage source employed in any particular case, any or all of the gap l8, the condenser 24, the resistances 25 audit and inductance 2'? of Figure 1 may be omitted, and a discharging circuit comprising a spark gap and a condenser, such as 25 and 2| Figure 1, connected in series with one another,

' tl iespark plug having electrodes, such as 5i and 52 Figure-5, spaced by insulation, such as 53 Figure 5, presenting between said electrodes a semi-conductive discharge path, such as 5 3 Figure 5, which may be comprised by a carbon or other deposit.

It is also a feature of the invention to provide 'for use in electrical ignition apparatus a spark plug comprising substantial inner and outer electrodes, such as 5| and 52 Figure 5, and mica insulation, such as 53 Figure 5, which is compressed tightly between said electrodes and has a deposit, such as 5 3 Figure 5, of carbon or other material on an exposed-surface thereof providing a semi-conductive discharge path between the electrodes;

The semi-conductive discharge path, so 54 Figure 5, may be formed by burning colloidal graphite on to an exposed surface of the insu- Q la-tion.

The compression of mica insulation, such as 53 Figure 5, between inner and outer electrodes,

such as 5i and 52 Figure 5, may be effected in any known or convenient manner, for example,

by placing the mica, such as 53, within an internally slightly tapering external electrode, such' as; 52, and then driving an externally slightly tapering internal electrode, such as 5!, into position withinit. It isfound that icy-having mica insulation tightly compressed between substantial electrodes the mica becomes eroded by repeated discharge via the semi-conductive path over thesurface of the mica in use, to a less extent than do the electrodes so that the improved spark plug has along useful life.

ch as H We claim:

1. Electrical ignition apparatus for use with an inductioncoil comprising acharge accumulating condenser, a charging circuit connectedtherewith including a relatively high voltage charging spark gap and input leads for connectionwith an induction coil, and, a discharging circuit connected with thechargeaccumulating condenser including a spark plug lead and a relativelylow voltage-discharging spark gap, wherebyiu operation thecharge accumulating condenser receives from an induction coil with which the input leads are connected and via the charging spark gap repeated unidirectional charging impulses corresponding to successive interruptions of the induction coil primary circuit and when the voltage of the accumulated charge thus built up on'the condenser becomes sufiiciently high saidcondenser discharges via the discharging gap, means being provided for reducing the potential difference obtaining between the electrodes of the charging gap whereby it is ensured that said gap is extinguished each time the induction coil voltage declines and-then changes polarity and opportunity for discharge of the charge accumulating condenser reversely through the charging gap is reduced. g

2. Electrical ignition apparatus for use with an induction coil comprising a charge accumulating condenser, a-- charging circuit connected therewith including a relatively high voltage charging spark gap and input leads for connection with an induction coil, and, a discharging circuit connected with the charge accumulating condenser including a spark plug lead and a relatively low voltage-discharging spark gap, whereby in operation the charge accumulating condenser receives from an induction coil with which the input leads are connected and via the charging spark gap repeated unidirectional charging impulses corresponding to successive interruptions of the induction coil primary circuit and when the voltage of the accumulated charge thus built up on the condenser becomes sufficiently high said condenser discharges via the discharging gap, there being connected in the charging and discharging circuits in series with the charge accumulating condenser a small inductance of such uncritical value in any particular case that in operation each time the charging gap breaks down a transient high frequency voltage is developed across said small inductance by the transient high frequency current which then flows in the charging circuit due to the self-capacity of the induction coil connected to the input leads and any added shunt capacity, whereby the accumulated charge voltage required to break down the discharging ii gap is made smaller and pre-break down corona and brush discharge losses in said gap are reduced, said small inductance also having the effect of limiting the peak discharge current through the discharging gap and acting in conjunction with capacity associated with the spark plug lead to augment the voltage produced at a spark plug with which the latter is connected. 3. Electrical ignition apparatus as claimed in claim 2, wherein series resistance is included in the charging circuit for the purpose of controlling the value of the transient high frequency-current and so also of the transient high frequency voltage developed across the small series inductance. 4. Electrical ignition apparatus as claimed in claim 1, wherein there is connected in thecharging and discharging circuits in series with the charge accumulating condenser a small inductance of such uncritical value in any particular case that'inoperat'ion each time the charging'igap breaks down a transient high frequency voltage is developed across said small inductance by the "transient high frequency current which then flows in the charging circuit due to the self-capacity of the induction coil'connectedto the input leads and any addedshuntcapacity, whereby the accumulated charge voltage required to break ddwn'the discharging gap is made smaller and "pre break :down corona :and brush discharge losses "in said; gap are reduced, said small inductance also having the eifect of limiting the peak discharge current through the discharging "gap and'acting in conjunction with capacity associated with the sparkplug lead to augment the voltageproducedjat a spark plug with which thelatter is connected.

15. Electrical ignition apparatus as claimed in claim 4, wherein series resistance is includedin the" charging circuit for the purpose of controlling the value of the transient high frequency current and'so also of the transient high frequency voltage developed across the small series inductance.

6. Electrical ignition apparatus for use with induction coil comprising acharge accumulating condenser, a charging circuit connected therewith including a relatively high voltage charging spark 51.13 andinput leads for connection with an induction coil,; and a discharging circuit connected with thecharge accumulating condenser including a spark pluglead and a relatively low voltage ,discharg-ing spark gap, whereby in operation the charge accumulating condenser receivesfroinan induct on w thj h he input ea a conn d a he e h r p rk ap. ;peated unidirectional-charging impulses corresponding to" successive interruptions of the induction coil primary circuit and when the voltage of the accumulated charge thus built upon the condenser becomes sufiiciently high said condenser discharges via the discharging gap, there a being connected across the input leads via a se- 1-16 resistance a small. auxiliary condenser, of 1 which latter and said series resistance the values fare uncritical, whereby it is ensured that the ging spark gap is extinguished each time the induction coil voltage declines and then 'i'changes polarityand opportunity for the charge *accuniulating condenser todischarge reversely through the charging gap is reduced.

FGElectricaI ignition apparatus as claimed in claim 6," wherein there is connected in the charging'arid discharging circuits in series'with the charge accumulating'condenser a small induct- "ance of such uncritical value in 'anyparticular" casethat inoperation each time the charging gap ated withthe spark plug lead to augment the voltage produced at a spark plug with which the latter is connected.

8. Electrical ignition apparatus as claimed in claim '7, wherein series resistance is included in the charging circuit for the purpose of controlling the value of the transient high frequency current and so also of the transient high frequency voltage developed across the small series inductance.

9. Electrical ignition apparatus as claimed in claim 6, wherein a small inductance is connected in series in the discharging circuit and a third spark gap, of which the-break down voltage is of the same order as that of the charging gap, is

connected between the small auxiliary condenser andthe'spark plug lead at that side of said small inductance remote from the charge accumulating condenser," whereby in operation each discharge at'a spark plug connected to the spark plug lead is initiated at relatively high voltage by energy from the small auxiliary condenser and break down of the discharging gap and discharge of the charge accumulating condenser follow. I

10. Electrical ignition apparatus as claimed in claim 6, wherein a high frequency transformer having primary and secondary windings and a third spark gap of which the break down voltage is :not substantially less than that of the charging gap are connected with said third gap and the transformer primary Winding in series with one another across the small auxiliary condenser and the transformer secondary winding in series with the discharging spark gap between the latter and the charge accumulating condenser.

11. Electrical ignition "apparatus comprising an induction coil, a spark plug'having electrodes spaced by insulation presenting a semi-conductive surface as a discharge path between said electrodesya charge accumulating condenser, a charging circuit connected with said condenser including a relatively high voltage charging spark gap and input leads connected with the induction coil, and, a discharging circuit connected with the charge accumulating condenser including a relatively low voltage discharging spark gap and a spark 'plug'lead connected with the spark plug,

whereby in operation the charge accumulating condenser receives from the induction coil via the charging spark gap repeated unidirectional char ing impulses corresponding to successive interruptions ofthe induction coil primary'circuit and when "the voltageofthe accumulated charge thus :built up on the"condenserbecomes sufficiently high said condenser discharges via the discharging gap and the spark plug, meansbeing provided "for reducing the potential diiierence obtaining between the electrodes of the charging gap whereby it is ensured that said gap is extinguishedeach time "the induction coil voltage declines-and then charges polarity and opportunity for discharge of the charge accumulating condenser reversely through the charging gap is reduced.

. .12. Electrical ignition apparatus as claimed in claim 11, wherein there is connected in the charging and discharging circuits in series with the charge accumulating condenser a small inductance of such uncritical value in any particular case that in operation each time the charging gapbreaks down a transient high frequency voltage is developed across said small inductance'by the transient high frequency current which then flows in the charging circuit due to the self-capacity of the induction coil connected to the input leads and any added shunt capacity, whereby the accumulated charge voltage required to break down'the discharging gap is made smaller and pre break downcorona and brush discharge losses in said gap are reduced, said small inductance also having the efiect of limiting the peak discharge current through the discharging gap and acting in conjunction with capacity associated with the spark plug lead to augment the voltage produced between the sparkplug electrodes.

- 1 13,: Electrical ignitionapparatus comprising an induction coil, a spark plug having electrodes spaced by insulation presenting a semi-conducincluding a relatively high voltage charging spark gap and input leads connected with the induc-, tion coil, and, a discharging circuit connected with the charge accumulating condenser including a relatively low voltage discharging spark gap and a spark plug lead connected with the spark plug, whereby in operation the charge accumulating condenser receives from the induction coil via the charging spark gap repeated unidirectional charging impulses corresponding to successive interruptions of the induction coil primary circuit and when the voltage of the accumulated charge thus built up on the condenser becomes sufficiently high said condenser discharge via the discharging gap and the spark plug, there being connected across the input leads via a series resistance a small auxiliary condenser, of which latter and said series resistance the values are uncritical, whereby it is ensured that the discharging spark gap is extinguished each time the induction coil voltage declines and then changes polarity and opportunity for the charge accumulating condenser to discharge reversely through the charging gap is reduced.

14. Electrical ignition apparatus as claimed in claim 13, wherein there is connected in the charging and discharging circuits in series with the charge accumulating condenser a small inductance of such uncritical value in any particular case that in operation each time the charging gap breaks down a transient high frequency voltage is developed across said small inductance by the transient high frequency current which then flows in the charging circuit due to the self-capacity of the induction coil connected to the input leads and any added shunt capacity, whereby the accumulated charge voltage required to break down the. discharging gap is made smaller and prebreak down corona and brush discharge losses in said gap are reduced, said small inductance also having the effect of limiting the peak discharge current through the discharging gap and acting in conjunction with capacity associated with the spark plug leadto augment the voltage produced between-the spark plug electrodes.

15. Electrical ignition apparatus as claimed in claim 14, wherein series resistance is includedin the charging circuit for the purpose of controlling the value vof the transient high frequency current and so also of the transient high frequency voltage developed across the small series inductance. V

164 Electrical ignition apparatus as claimedin claim 13, wherein a small inductance ,is connected in series in the discharging circuit anda third spark gap, of which the break down voltage is of the same order as that of the charging gap, is connected between the small auxiliary condenser and the spark plug lead at that side of said small inductance remote from the charge accumulating condenser, whereby in operation each discharge at the spark plug is initiated-at relatively high voltage by energy from the small auxiliary condenser and break down of the'discharging gap and discharge of the charge accumulating condenser follow.

17. Electrical ignition apparatus as claimed in claim 13, wherein high frequency transformer having primary and secondary windings and a third spark gap of which the break down voltage is not substantially les than that of the charg ing gap are connected with said third gap and the transformer primary winding in series with one another across the small auxiliary condenser and the transformer secondary winding in series with the discharging spark gap between the latter and the charge accumulating condenser.

18. Electrical ignition apparatus as claimed in claim 11, wherein the spark plug has substantial inner and outer electrodes and mica insulation compressed tightly between said electrodes to prevent erosion of the mica, the exposed surface of the mica being treated to provide a semi-conductive discharge path between the electrodes.

19. Electrical ignition apparatus as claimed in claim 13, wherein the spark plug has substantial inner and outer electrodes and mica insulation charge accumulating condenser a small inductance of such uncritical value in any particular case that in operation each time the charging gap breaks down a transient high frequency vouage is developed across said small inductance by the transient high frequency current which then flows in the charging circuit due to the selfcapacity of the induction coil connected to the input leads and any added shunt capacity, whereby the accumulated'charge voltage required to break down the discharging gap is made smaller and pre-break down corona and brush discharge losses in said gap are reduced, said small inductance also having the effect of limiting thev peak discharge current through the discharging gap and acting in conjunction with capacity associated with the spark plug lead to augment the voltage produced at a spark plug withwhich the latter is connected.

7 21. Electrical ignition apparatus as claimed in claim 20, wherein series resistance is included in the charging circuit for the purpose of controlling the value of the transient high frequency current, and soalso of the transient high frel5- duencyvoltage developed across the small series inductance.

2-2. Electrical ignition apparatus comprising a condenser, a charging circuit connected. with said condenser, and a discharging circuit. connected with said condenser, said discharging. circuit including an enclosed and sealed type spark gap-and aspark'plug connected in series withone another, and the: spark plug having electrodes spacedfby insulation presenting a semi-conductive-discharge path between said electrodes.

23. Electrical ignition apparatus as claimed in claim 22, wherein the spark plug has substantial inner and outer electrodes and mica insulation which. is: compressed tightly between said electrodes and .is. treated at an exposed surface there.- of to: present the semieconductive discharge path.

24. Electrical ignition apparatus as claimed in claim 23, wherein the semi-conductive discharge path iscomprised by carbon on an exposed surface of the mica insulation of the spark plug.

25. Electrical ignition apparatus as claimed in claim .2f-l,..wherein the semi-conductive discharge path is formed. by burning colloidal. graphite on to an exposed surface of the mica. insulation of the spark plug.

26. Electrical. ignition apparatus for use with aninduction coil arranged to have current impulses .flow therethrough, said apparatus comprising a charge accumulating condenser, a charging circuit containing a charging spark. gap, and meansv comprising resistance and capacitancel for reducing the potential difference obtaining between the electrodes of the charging gap, Wherebyit is ensured that said gap is extinguished each time the induction coil voltage declines and then changes polarity, and a discharging circuit comprising an ignition device and. including an inductance and associated sparking gap arrangement fo controlling discharge through the discharge circuit.

:275. Electrical ignition apparatus for use with an induction coil arranged to have current. impulses flow therethrough, said apparatus comprising a charge. accumulating condenser, a charging circuit containing. a. charging spark gap, and a discharging circuit comprisingan .ignition.device and including an inductance'and associated sparking. gap arrangement for controllingdischar-ge through the discharge circuit.

.28. Electrical ignition apparatus for use. with aninduction coil arranged to. have current impulsescfiow .therethrough, said apparatus) comprising aeharge accumulating condenser, an induction coil, a chargingcircuit comprising a relatirelyhighvoltage charging spark gap connected in series. relation to the coil and condenser, a discharging circuit connected across the charge accumulating condenser including a. spark plug lead, a spark gap means and inductive means therein for controlling discharge through the discharge cricuit, thecharging spark gap permitting; successive, impulses from the coil to build up a charge in the accumulating condenser before the said discharge. is established, and means comprising resistance and capacitance in the charging circuit for reducing-the potential difference obtaining between the electrodes of the charging gap whereby it is ensured that said gap is extinguished each time the induction coil voltage declines and then changes polarity and opportunity for discharge of the charge accumulatmg condenser reversel-y through the charging gap is reduced.

:29. T'Electrical ignition apparatus comprising an induction coil, a. spark plug having electrodes.

spaced by insulation presenting a semi-conductive surface as a discharge path between said electrodes, a charge. accumulating condenser, a charging circuit connected with said condenser including areiatively highvoltage chargingrspark gap and input leads. connected. with the inductioncoil, and, a discharging circuit connected with the charge accuinualting condenser including a relatively low voltage discharging. spark gap and a spark plug lead connected with the spark plug, whereby in operation the charge accumulating condenser receives from the induction coil via. the chargingspark gap repeated unidirectional charging impulses corresponding to successive interruptions of the induction coil primary circuit and when the voltage of the accumulated charge thus built up on the condenser becomes suflicientlyhigh said condenser discharge via the discharging gap and the spark plug, there being connected across the input leads via a series. resistance a small auxiliary condenser, of which latter and said series resistance the values are uncritical, whereby it is ensured that the discharging spark gapis extinguished each time the induction coil voltage declines and then changes polarity and opportunity for the charge accumulating condenser to discharge reversely through the charging gap is reduced, the spark plug having substantially inner and outer electrodes and mica insulation comprisedtightly between said electrodes to prevent erosion of the mica, the exposed surface of the mica being treated to provide a semi-conductive discharge path betweentthe electrodes, a small inductance connected in series in the discharging circuit and a. third. spark gap, of which the breakdown voltage is not substantiallylessthan that of the charging gap, connected between thesmall auxiliary condenser and the spark pluglead at that side of said small inductance remote from the charge accumulating condenser, wherebyin operation each dischargeata spark plug connected to the spark plug lead is initiated at relatively high voltage by energy from the small auxiliary condenser and break down of. the discharging gap and discharge of. the charge accumulatinglcondenser follow.

30. Electrical ignitionapparatus coznprisingan induction coil, a spark plug having electrodes spaced by insulation presenting a semi-conductive surface as a discharge path between said. electrodes, a. charge accumulating. condenser, a charging circuit connected with said condenser including a relatively high voltage charging spark and input leads connected with the induction coil, and, a discharging circuit connected withthe charge accumulating condenser including a relatively low voltage discharging spark gap and a spark plug lead connected with the spark plug, whereby in operation the charge accumulating condenser receives from the induction coil via charging spark gap repeated unidirectional charging irnpulses corresponding to successive interruptions of the induction coil pri mary circuit and when the voltage of the accumulator charge thus built up on the condenser becomes suiiiciently high said condenser discharge via the discharging gap and the spark plug, there being connected across the input leads via a series resistance a small auxiliary condenser, of which latter and said series resistance the values are uncritical, whereby it is ensuredthat the discharging spark gap is extinguished each time the induction coil-voltage declines and then changes polarity and opportunity for the charge accumulating condenser to discharge reversely through the charging gap is reduced, the spark plug having substantial inner and outer elec trodes and mica insulation comprised tightly between said electrodes to prevent erosion of the mica, the exposed surface of the mica being treated to provide a semi-conductive discharge path between the electrodes, and a high frequency transformer having primary and secondary wind-- ings and a third spark gap of which the break down voltage is not substantially less than that of the charging gap being connected with said third gap and the transformer primary winding in series with one another across the small auxiliary condenser andv the transformer secondary winding in series with the discharging spark gap between the latter and the charge accumulating condenser.

31. Electrical ignition apparatus comprising a condenser, a charging circuit connected with said condenser, and a discharging circuit connected with said condenser, said discharging circuit including an enclosed and sealed type spark gap and a spark plug connected in series with one another, and the spark plug having electrodes spaced by insulation presenting a semi-conductive discharge path between said electrodes, the semi-conductive discharge path being comprised by a deposit upon the exposed surface of the insulation of the spark plug.

WILLIAM RICHARD DEBENHAM. JOHN CLIFFORD SHENTO'N.

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

UNITED STATES PATENTS Number Name Date 1,962,669 Parkin June 12, 1934 2,017,364 Anderson Oct. 15, 1935 2,930,228 Randolph et al Feb. 11, 1936 2,456,475 Wargin Dec. 14, 1948 2,497,307 Lang Feb. 14, 1950 FOREIGN PATENTS Number Country Date 536,460 Great Britain May 15, 1941

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