US3534722A - Capacitor discharge ignition system - Google Patents

Description

United States Patent Inventor Bob 0. Burson East Longmeadow, Massachusetts Appl. No. 758,562 Filed Sept. 9,1968 Patented Oct. 20, 1970 Assignee R.E. Phelon Company, Inc.

East Longmeadow, Massachusetts a corporation of Massachusetts CAPACITOR DISCHARGE IGNITION SYSTEM 5 Claims, 1 Drawing Fig.

u.s.c| 123/148,

123/149 1m. 01...; l. F02p1/02 FieldofSearch ..123/148(DC),

148(E),148(AC).148(C). 1481B). 149(A),149(D); 315/2l8,209(CD) [56] References Cited UNITED STATES PATENTS 1,513,551 10/1924 Hawkins a 123/148AC 3,358,665 12/1967 Carmichael et a1 123/148E 3,447,521 6/1969 Piteo 123/148E Primary Examiner-Laurcnce M. Goodridge Aziorney- McCormick. Paulding and Huber ABSTRACT: A capacitor discharge ignition system includes a surgetype transformer for converting the discharge surge current of the capacitor from a low to a high voltage and wherein the primary winding is physically separated from the secondary winding to reduce winding-to-winding capacitance and to thereby produce greater conduction of the surge current through the primary winding to obtain a longer duration spark.

Patented Oct. 20, 1970 3,534,722

IN VEN TOR.

Bob O Bursa/7 MM4 ATTORNEYS CAPACITOR DISCHARGE IGNITION SYSTEM BACKGROUND OF THE INVENTION This invention relates to ignition systems for spark-ignited engines, and deals more specifically with such a system wherein a capacitor is periodically charged and discharged to provide the power for the spark.

Capacitor discharge ignition systems, as well as other ignition systems, commonly employ a step-up transformer or ignitio'ncoil for converting a low voltage current in a primary winding of few turns to a high voltage across the ends of a secondary winding having a very much larger number of turns. To obtain asclose an inductive coupling as possible between the two windings, and therefore as high an output voltage as possible, it has been customary to wind one of the windings directly on top of the other, and also the iron core on which the windings are wound is usually, particularly in inductive ignition systems, fashioned to provide a discontinuous iron circuit for the flux so that the flux rapidly collapses to zero when the primary current ceases.

In the use of capacitor discharge ignition systems, however, it has been noted that they in general produce a relatively short duration of spark, and this has caused some problems where long-duration sparks are desirable as with particular types of engines or engines operating at low temperature, The basic object of this invention is therefore to improve the firing duration of capacitor discharge ignition systems, and this object has been accomplished by discovering that the firing duration is improved by utilizing a differently designed transformer than previously used in such systems and wherein the primary winding is physically separated from the secondary winding thereby sacrificing some inductive coupling but also reducing the winding-to-winding capacitance, the latter of which has a very favorable influence. As an added advantage this arrangement also reduces the amount of copper or other winding material required by reducing the mean length of each winding turn.

SUMMARY OF THE INVENTION The invention resides in a capacitor discharge ignition system wherein a capacitor is repeatedly charged from a relatively low voltage source of power and discharged through the primary winding of a step-up surge transformer to create a high voltage applied to the spark plug or other spark gap device. The transformer includes a continuous iron core, such as a rectangular one having four legs, with the two windings being located at spaced points along such core to substantially reduce the winding-to-winding capacitance as compared to transformers previously used in such systems.

BRIEF DESCRIPTION OF THE DRAWING The single FIG. of the drawing is a schematic diagram illustrating a capacitor discharge ignition system embodying this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning to the drawing, the single FIG. of the drawing illustrates schematically a capacitor discharge ignition system embodying this invention and which, except for the transformer utilized therein, is or may be substantially similar to the capacitor discharge ignition system shown and described in my copending US. Pat. application, Ser. No. 675,429, filed Oct. 16, 1967, and entitled Inductively Triggered Breaker less Ignition System with Automatic Spark Advance. Reference may be had to said copending application for a more complete understanding of the illustrated system, however, for the present purposes, it may be noted that the system includes a capacitor which is repeatedly charged and discharged to produce the power for the spark at the associated spark gap ignition device, illustrated at 22 and which may be a commonspark plug.

The power source from which the capacitor 20 is charged constitutes a winding 24 of an alternator including a flywheel 26 containing one or more permanent magnets with associated pole shoes which are rotated past the coil 24 so as to produce voltage pulses of alternating polarity therein. A diode 28 connected in parallel with the coil 24 rectifies the voltage pulses induced in the coil 24 so that only positive pulses are transmitted to the condenser 20, and another diode 30 connected in series with the coil 24 prevents the charge on the condenser 20 from returning to the coil 24 during the negative portion of each cycle.

The condenser 20 is also connected in parallel with the primary winding 32 of a surge type step-up transformer, indicated generally at 34, through a silicon-controlled rectifier 36 which controls the discharging of the capacitor through the primary winding 32. The conduction of the silicon-controlled rectifier is controlled by triggering signals induced in a triggering winding 38 connected between its gate terminal and cathode, as shown. Therefore, when the condenser 20 is charged by one or more positive pulses supplied from the alternator coil 24 and the silicon-controlled rectifier 38 thereafter triggered from a nonconducting to a conducting state, the condenser 20 is discharged through the primary winding 32 of the transformer 34 to produce a surge of current through the primary winding which induces a high voltage in the secondary winding 40 and accordingly produces a spark at the spark plug 22 connected to the secondary winding 40. The triggering signals induced in the triggering coil 38 may be produced, as explained in my copending application, Ser. No. 675,429, by a permanent magnet 42 on which the coil is wound and which is placed so as to cooperate with a pin 44on the periphery of the flywheel 26 to induce a varying flux through the coil in response to the rotation of the flywheel with one triggering pulse being produced each time the pin 44 passes the magnet 42 and coil 38.

As shown by the drawing, the surge transformer 34 used for converting the discharge surge current of the capacitor 20 to a high voltage differs from the type of transformers customarily used in capacitor discharge ignition systems in that the prima ry and secondary windings 32 and 34 instead of being wound one on top of another are physically spaced from one another as by, in the illustrated case, being located on opposite legs 46 and 48 of the four-legged continuous iron core 50. This physical separation of the two windings reduces somewhat their inductive coupling which is contrary to the previous belief that the inductive coupling should be as large as possible. How ever, it also eliminates, or at least very drastically reduces, the capacitance between the two windings, and this has been discovered to create a very desirable influence on the duration of the spark produced at the spark plug 22 by prolonging such duration.

The reason for the prolongation of the spark produced by the capacitively decoupled transformer 34 is believed to reside in the fact that the absence of the winding-to-winding capacitance causes a greater portion of the power stored in the capacitor 20 to pass through the primary winding 22 and produce a useful output from the secondary winding 40. This in turn is due to the fact that the surge of current discharged from the capacitor 20 has a very steep initial rise portion containing very high frequency components. When a winding towinding capacitance is present as in previous transformers, this capacitance, in series with the capacitance of the secondary winding 40, forms a short circuit for these high frequency components, and therefore an initial portion of the surge is largely dissipated through this short circuit without passing through the primary winding. The elimination of the windingto-winding capacitance eliminates this short circuit and allows the system to utilize effectively the initial portion of the pulse which contains a considerable amount of power.

Although, as mentioned, the physical separation of the primary and secondary windings does somewhat degrade their inductive coupling, by placing both of the windings on a continuous iron core, such as the core 50, this degradation is kept at a minimum and has proved to be oflittle or no significance. In addition, the physical separation of the two windings, as shown, has the further advantage of reducing the total amount of copper or other winding material required for the windings in that the mean length of each winding is reduced. That is, the turns of the winding which would otherwise be wound on top of the other winding are considerably shorter clue to being wound on a smaller body.

lclaim:

1. In a capacitor discharge ignition system for a spark-ignited engine having a spark gap ignition device the combination comprising: a capacitor, a step-up surge transformer hav ing primary and secondary windings, means for repeatedly charging said capacitor from a source of power, and means operableafter each charging cycle of said capacitor for suddenly discharging it through said primary winding to produce a surge of current in said primary winding inducing a high voltage in said secondary winding for application to said spark gap ignition device, said means operable after each charging cycle of said capacitor for discharging it through said primary winding including a triggered electronic switch device connected between said capacitor and said primary winding for controlling the flow of current from said capacitor to said primary 'winding and means connected with said triggered electronic switch device for producing triggering signals for triggering said electronic switch device from a noncondueting state to a conducting state, said transformer including an iron core and said primary and secondary windings being located on said core at locations spaced from one another so as to be substantially capacitively decoupledl i V I 2. The combination defined in claim 1 further characterizec l by said iron core'being in the form of a continuous closed loop.

3. The combination defined in claim 1 further characterized by said transformer core being in the form of a four-legged loop with said primary and secondary windings being located respectively on two opposite ones of said legs.

4. The combination defined in claim I further characterized by said capacitor being connected in parallel with said source of power and said triggered electronic switch device comprising a silicon-controlled rectifier connected in series with said primary winding between said primary winding and i said capacitor.

5. In a capacitor discharge ignition system for a spark ignited engine having a spark gap ignition device the combination comprising: a capacitor, a step-up surge transformer having primary and secondary windings, means for repeatedly charging said capacitor from a source of power. and means operable after each charging cycle of said capacitor for suddenly discharging it through said primary winding to produce a surge of current in said primary winding inducing a high voltage in said secondary winding for application to said spark gap ignition device, said means operable after each charging cycle of said capacitor for discharging it through said primary winding including a triggered electronic switch device connected between said capacitor and said primary winding for controlling the flow of current from said capacitor to said primary winding and means connected with said triggered electronic switch device for producing triggering signals for triggering said electronic switch device from a non-conducting state to a conducting state, said primary and secondary windings of said transformer being physically separated from one another so as to have a very low value of windingto-winding capacitance.

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