CA1044751A - Continuous-wave high-frequency ac ignition system - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
An ignition system which employs an inverter to develop a continuous-wave high-frequency spark signal from a DC supply. The inverter employs a single transformer with a high-voltage output winding and a pair of transis-tors coupled to an input winding plus a feedback winding.
There is a saturable-core inductor also coupled to the transistors for causing a frequency shift in the inverter AC signals under load conditions in the spark-signal out-put.

Description

3L~44~75~

This invention concerns ignition systems for in-ternal combustion engines in general, and more specifically relates to such a system that employs high-frequency contin-uous-wave AC signals to produce a controlled spark duration for each ignition. It particularly employs only a single transformer. And, it includes means for causing a frequency shift as the output circuit of the oscillator changes from no-load to load conditions.
Heretofore, there have been a considerable number ;-of proposed arrangements that pu~portedly would employ AC
spark signals for internal combustion engines, and the like.
However, in such prior arrangements, there have been diffi-culties in the practical applications~ An important aspect of such difficulties related to the ability of such systems . ~ .
to start the oscillation at the instant when a spark si~la:l .'; ',' ~:

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is called for. While the applicant has earlier overcone :
that particular diffic~ty in some of the inventions de~
scribed in the foregoing Canadian applications, they did not provide for a beneficial improvement which was only recognized in connection with a two-transformer type of oscillator or inverter. Such beneficial improvement re-lates to the ability to incr~ase the initii~l voltage amplitude along with substantial reduction thereof upon striking a spark. This invention teaches how that concept may be applied to a single-transformer type of inverter. `-. .
Consequently, this invention is particularly con-.
cerned with a single-transformer, continuous-wave, high-frequency AC ignition system which includes an inverter with means for shifting the oscillation frequency from no-load : , to load conditions as the spark load appears in the output circuit of the inverter.
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SUMMARY OF THæ INVE~TIO~
Briefly, thisi invention concerns an ignition sys-tem for an internal combustion engine which system comprises an inverter including a single transformer having a second-~, ary winding for supplying a continuous-wave high-frequency ~, spark-signal output, only during controlled sparking inter-vals. It also comprises a primary winding with at least one , transistor connected in circuit therewith, and a fee~back winding connected to said transistor for providing an oscil-lator having a predetermined load frequency during said sparking intervals. The said load frequency is substantial-ly different from a harmonic frequency of the fundamental ', resonant frequency of said secondary winding circuit. Also, ~ ;~
'~ 30 the inverter includes saturable-core inductor means connected in circuit with said feedback winding for determining the ,''''" ~ ;:

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no-load ~requency to be sub~tantially equ~l to said harmonic frequency.
Again, brie~ly, the inventlon relates to a com-binatio~ Nith a continuous-wave hi~h-frequency ignition ~y8-tem wherein sald ~ystem comprise~ a single transformer hav-lng a high-~oltage A~ ~park-signal output windlng, and an input windin~ on said tra~sformer. It also comprlses a feedback windlng on ~aid tra~former~ a co~trol winding on said transformer, and a ~air of transi~tors. It al~o com-prises first circult m~ans ~or connecting said ~ran~i~tors to ~aid input and feedback windings to for~ a ~quare-wave high-frequency oscill~tor, and second circuit means ~or con-necting a DC source of power to ~aid oacillator. In uddi-tion~ it compri~es a saturable-core inductor~ and third circuit means for connecting ~aid inductor into eald o~cil- ;~
lator ~he~eby the no-load frequency equal~ a ha~monic of -th~ ~undamenta~ re~onant freguency of said output-~inding circult. The said load fraquancy is substantlally differ-ent fro~ said harmon~c frequency. `~
DESCRrPTION OF TÆ DRAWT~G
~he foregolng and other ob~ects and bene~it~ of the inve~tion ~ill b~ ~ore fully set forth below in cQn-~ection ~h the best mode cont~mplat~d by the inventor o~
c~rrying out the in~enti~n~ and ln connection with which there~e illu~trati~n~ pr~v~ded in the dr~wing, wherein:
The FIGURE of draw~ng 1llustrate~ a sch~matic circuit diagram o~ an ignition 8y8tem ~ccordtng to the ~n- ;
ventlon. ` ;
D~SCRIP _ON OF TNE PRE~ERRED EM~OD~ME~T
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AB indlcated above, it ~hould be understoo~1 that thl~ ~nvention i3 s~milar ~n baslc princtple~ to that sho~n ..
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and described in my United States Patent 3,847,129 issued November 12, 1974. However, in that case, the inverter circuit employed two transformers, and the parameters of both were adjusted for setting the desired frequency shift conditions. In this invention, the ability to obtain sim-ilar results was not subject to mare application of the teachings of the prior art. Thus, while a single-trans-former inverter system had the advantages of reduction in cost and a compact structure, the ability to strike a spark by extra high initial voltage without adversely affecting power requirements was lacking.
Referring to the FIGURE of drawings, it will be observed that the schematic circuit diagram illustrates an ignition system. It includes a single transformer 11 that has a high-voltage secondary winding 12 which is connected to a ground or common circuit at one end. The other end is connected to a spark-signal circuit which may be for an in-ternal combustion engine (not shown). This is indicated by the caption "HIGH VOLTAGE TO DISTRIBUTOR CAP" ad~acent to a circuit connection 13.
The transformer 11 also has a center-tapped pri-mary winding 16 and a separate feedback winding 17 as well as a control winding 18 thereon.
There is a source of DC power which may be a bat- ; , tery 23, as indicated. This, of course, may be a standard ~ ~
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automotive battery, e.g., one providing a 12-volt supply, -~
or it may be a 24-volt type battery. Battery 23 is con-nected into the circuit with one terminal grounded, as in-dicated at reference no. 24. The other terminal is con-nected via circuit connections 27 and 20 to a center tap 29 on the transformer primary winding 16. Also, there is a ,' ' .
'":,,' ~' capacitor 30 that is connected between the circuit connec-tion 28 and ground. It is imp~rtant th,at the capac~tor 30 be physically located close to the centler tap~9. Its pr~
pal purpose is to nulli~y the effect~ of the impedance of the conductor 28 and the internal impedance of the battery 23~ -Connected to the endsi of primar~ winding 16 are the collector electrodes of a pair of transistors 33 and 34. The emitter electrodes of the~ie transist~ are each - . .
connected to ground j9 as indlcated by re~erence n~mbers 35 and 36, respectively. The base electrodes o~ the transls-tors 33 and 34 are connected to the ends of the f'eedback winding 17, via circult connect~ons 39 and 40~ respective-ly. Included in the foregoing base drive circuit ~rom feed-ba~k winding 17, there is a resis~or 41 for partially de- ~:
termining the 03iclllator frequency. Also, it may be noted that connected between each of the base electrode~ of tran~
sistors 33 and 34 and ground~ there are diodes 43 and 44, `~
respectively, which act to protect each transistor against 20 harmful raverse voltage that may be applied between its base ~ ;
electrode and ground . As indicated above, the capacltor 30 acts to supply initial energy to the transistors when they conduct, and this ccmpensates for the voltage drop that de-vel~l?s due ~o the high current which they draw. Consequen~
ly~, an ou~put voltage ln ~he secondary ~inding 12 is of ~:~greater magnitude than ~ould otherwlse be the case.
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~',In order to control the starting and 5 tolpping of oscillation of the ~oreg~g inverter circult, the control ;~
winding 18 is included on the transfor~ner 11. This type of .. . . . .
30 inverter (o~cillator ), as ~pplied to ignition syst~ms 3 has been described in r~ above-noted application Ser:ia.l ~o.
'I .
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191,913 filed Feb. 6, 1g74 It has a DC bîas current ; ~ -applied to the control winding i8 during the nono3cillating.
periods. Simultaneously, there i~ a lo~-impedance path con~cted across the winding 18.
The DC bias current i~ applied vla an ignition switch 46 that has a pair of stationary term1nals 47 which ~ -are hoth connected directly to the ~oæitive terminal of:, . . .
battery 23 via a circu~t connecti~n 48. When the mo~able .. . . . . . . .
switch arm of switch 46 is placed i~to electrical contact with either o~ the terminal~ 47 (for start or run cond1-~ions), the battery voltage from battery 23 is connected over the circuit connection 48 a~d on via a connection 49 to a resistor 50 and a diode 51 to a circult connection polnt 52.
Fr~m the clrcuit polnt 52 the circuit carrying DC
battery potential co~tinues via illu~trated circuit conn~c~
tions 55 and 56 to one end o~ the control windlng 18. Th~
other end o~ winding 18 is connected via c~rcuit c~nnection~
59 and 60 to one diagon~l pcint 58 of a diode bridge 61.~An ~.
ad~acent diagonal 62 i~ connected via a circuit connection ~ .. , ~ ~,, .
63 to the collector electrode of a transistor 64 which acts as an electronic switch. The emi~ter electrode o~ transis-tor 64 ~s connected to ground, as indicated by a reference -~
number 67. ~ I
It will be noted that this complete a circuit ~ :
~r~m the battery 23 for appllcatlon o~ a DC b~.as current . .
.. . ..... .. . .
throu~h the control wind~g 18 whenever tl~e transistor 64 is conducting. ~he latter condition læ controlled by engine- -.
tl~ed contrc~ls, a~ lndlca~ed by the captio~ ad~acent to 30 the base clrcuit input to the tran31ætor 64.
Slmultaneously with the DC bias current f:low .
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throu~h control wlnding 18, i.e., when th~ translstor 64 is conducting, there is a low-i~pedance AC circuit across the winding that permiks induced AC signals (from the oscilla-tor) to load down the oscillator so that it will not o~cil-late. These nonoscillating conditions are created in be-tween spark-signal intervals so that the oscillator remain~
shut down, and no high-voltage7 spark-producing signa~ will be developed until the desired time for each engine con- :
trolled instant that is related to the spark lnterval for each cyllnder of an internal combustion engine.
As indicated above, this inverter circuit acts.
as a square-w~ve o~cillator which generate~ high-voltage continuous-wave spark signals in the secondary winding 12 at desired instants ~or controlled intervals o~ time. me :
interval~ are controlled by the control winding 18 which :;
stops the oscillations when a low-impedance AC circu~t is applied ~cro~ the wind~ng. Suc~ low-impedance AC circuit across control winding 18 includes a dlode bridge 61 and al60 a Zener dlode 70 that is connected between the circuit .
, .,,. i point 52 and a diagonal point 71 on the bridge 61.
In this manner~ whenever the tran~lstor 64 is ~ .
conductlng~ it provides a low-impedance AC path across the winding 18 which may be traced as ~ollows. Begirmi~g at the lower end (as viewed in the drawi~g) ~f winding ~8 and going vla connections 59 an~ 60 to th~ bridge 61, current :
flowing in such downward direction will have a low impedance path via the upper le~t-hand diode of the bridge 61 a~d the ~ -circuit co~nectiQn 63 to-an~-t~rQ~gh-the tr4~$~:s~,o~ ~4 and ~, khe ground connection 67. A return circui~ contlaues vla t~o paralle~ paths. me pr~mary path goes via a ground con-nection 74, a diagonal po~nt 75, dlode 78, diagoaal polnt 71, ~ , . .' ,.
. , ,: ' .
;' -a conductor 79, Zener diode 70, and then via connections 55 and 56 to the other side of the winding 18. The other re turn circuit path goes from the ground connection 2~ to the -battery 23 and then via the circuit connections 27 and ~8 to the switch 46 (now closed). Then it continues via the connection 49, the resistor 50, the diode 51, the connec-tions 55 and 56 to the other side of the winding 18.
On the reverse half-cycles of induced voltage in winding 18, the low-impedance path for return current flo~
in the opposite direction may be traced via connections 56 and 55 to the circuit point 52. The path then continues through the Zener diode 70 (breakdown voltage exceeded) to the diagonal point 71 on the bridge 61 and then through the ;
lower left-hand diode of the bridge 61 to the diagonal point 62. From point 62 it continues over the connection 63 to i the transistor 64 and, thence, via the ground connection 67 ;~
back through another ground connection 74 to an opposite diagonal point 75 on the bridge 61. From that point it may be traced over a resistor 76 and a diode 77 to the diagonal point 58 and on via the connection 60 and the connection 59 to the other end of winding 18.
It may be noted in passing that there are addi-tional capacitors, e.g., capacitors 80, 81 and 82, provided for radio-frequency by-pass. This is important since the oscillator is a square-wave type which consequently gene- ;~
rates substantial amounts of radio-frequency energies.
The details of the operation of a system like that described so far, have b~en fully set forth in my earlier re- ~
' lated Canadian application Serial ~o. 191,913. That appli- -cation explains the action of the control winding in stopping oscillation while setting the core of the transformer so , S~
that when the DC bias is removed -the oscillator will always start positively and instantaneously. Also~ it may be noted that the engine-timed control signals which are applied to the base electrode of the transistor 64, might be derived from various sources. For example, see my Canadian appli-cation Serial No. 169,583. This invention is particularly concerned with improved results that are obtained from the use of a saturable-core inductor 85. This inductor 85 is connected into the oscillator circuit and across the .'. ~: .
feedback winding 17. It is also connected between the base electrodes of transistors 33 and 34.
By determining the particular parameters related to the structure of the core and winding for inductor o5, the frequency of the oscillator may be controlled since the inductor can be made to saturate at a desired frequency.
In this manner, the open circuit oscillating frequency of the system may be set to match a harmonic frequency o~ the fundamental resonant frequency that exists in the output circuit to which winding 12 is connected. At the same time the power rating of the transistors 33 and 34 may be chosen along with the primary-to-secondary turns ratio of the trans-: ,:
former and the primary inductance under load, so that ade-quate spark-plug current can be supplied.
In the foregoing manner, the no-load or striking -voltage at the output of windlng 12 is increased a `
substantial amount by the resonant effect, in the manner that has been explained in my above~mentioned United States Patent No. 3,847,129. However, when that concept is applied to a single-transformer system, the ~ -ability to obtain adequate power in the spark signal after '; ' ''''' ' ' .~ '' '` .' _ g _ . :
, ' .

a spark is struck, i~ impaired unless a saturable-core in-ductor according to this inventlon is e~ployed. This is because the ad~u~tment o~ the prlmary in.ductance of the transformer would raise the impedanc~ and, consequently, reduce the power that could be delivered. But ~uch adverse ad~ustment ls not nece~sary when a saturable-cors inductance i8 employed. ;
Wh~le the invention has been described abo~e in ~.
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considerable detail and in accordance with the appl~cable :i statutes, thls is not in any way to be taken as limiting the invention, but merely as being descriptive thereof~
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Claims (7)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Ignition system for an internal combustion engine, comprising an inverter including a single transformer having a secondary winding and a circuit for supplying a con-tinuous-wave high-frequency spark-signal output from said secondary winding only during controlled sparking inter-vals, a primary winding with at least one transistor con-nected in circuit therewith, and a feedback winding con-nected to said transistor for providing an oscillator having a predetermined load frequency during said spark intervals, said load frequency being substantially different from a harmonic frequency of the fundamental resonant fre-quency of said secondary winding circuit, and saturable-core inductor means connected in cir-cuit with said feedback winding for determining the no-load frequency to be substantially equal to said harmonic fre-quency,

2. Ignition system according to claim 1, further comprising an oscillator-control winding on said transformer, and means controlled by said engine for connecting a loading circuit to said control winding and for applying a DC bias thereto between said sparking intervals whereby re-moval of said DC bias and said control winding load causes instantaneous starting of said oscillator.

. 11 .

3. Ignition system according to claim 2, wherein said primary winding is center-tapped with two transistors connected in circuit therewith, and said feed-back winding is also connected to said two transistors.

4. Ignition system according to claim 3, wherein each of said two transistors has the collector-emitter circuit across half of said primary winding, and said feedback winding is connected to the bases of both said transistors.

5. Ignition system according to claim 4, wherein said saturable-core inductor means is connected across said bases.

6. Ignition system according to claim 5, wherein said inverter also includes circuit means for connecting a DC source between said primary winding center tap and said collector-emitter circuits at a point between said transistors.

7. In combination, a continuous-wave high-fre-quency ignition system, wherein said system comprises a single transformer having a high voltage AC
spark signal output winding, an input winding on said transformer, a feedback winding on said transformer, a control winding on said transformer, a pair of transistors, first circuit means for connecting said transis-tors to said input and feedback windings to form a square-wave high-frequency oscillator having a predetermined load frequency, second circuit means for connecting a DC source of power to said oscillator, . 12 .

a saturable core inductor, third circuit means for connecting said inductor into said oscillator whereby the no-load frequency equals a harmonic of the fundamental resonant frequency of said output winding circuit, said load frequency being substantially different from said harmonic frequency.
. 13 .