US3741185A

US3741185A - Capacitor discharge ignition system

Info

Publication number: US3741185A
Application number: US00159610A
Authority: US
Inventors: T Swift; E Brayley
Original assignee: Eltra Corp
Current assignee: Prestolite Electric Inc
Priority date: 1971-07-06
Filing date: 1971-07-06
Publication date: 1973-06-26
Anticipated expiration: 1990-06-26
Also published as: GB1357688A; CA952975A

Abstract

A flywheel alternator with permanent magnet energization is disclosed for general power purposes which has combined with it charging means for a capacitor or capacitors for a capacitordischarge distributor-less ignition circuit or circuits suitable for use with single or multiple cylinder engines, wherein separate trigger coils are energized by a separate permanent magnet rotated with the flywheel to control the timing in the ignition circuit or circuits. The separate permanent magnet energizing the trigger coil or coils is provided with an automatic ignition advance device, which changes the ignition timing in accordance with variations in speed.

Description

United States Patent [1 1 Swift et al.

[ CAPACITOR DISCHARGE IGNITION SYSTEM [75] Inventors: Thomas E. Swift, West Springfield;

Elwin J. Brayley, East Longmeadow, both of Mass. [73] Assignee: Eltra Corporation, Toledo, Ohio [22] Filed: July 6, 1971 [211 App]. No.: 159,610

[52] US. Cl. 123/148 E, 123/149 R, 123/149 D [51] Int. Cl. F02p 3/06 [58] Field of Search 123/148, 149

[56] References Cited UNITED STATES PATENTS 3,560,833 2/1971 Oishi et al. 123/148 E 3,620,200 11/1971 Stephens 123/148 E 3,367,314 2/1968 I-lirosawa et a1. 123/148 E 3,646,605 2/1972 Plume 123/148 E 3,461,851 8/1969 Stephens 123/148 E To 1 BATTERY 54 R 5 1, M I CR 10 a ll June 26, 1973 3,324,841 6/1967 Kebbon et a1 123/149 R 3,599,616 8/1971 Oishi 123/148 E Primary Examiner-Laurence M. Goodridge Assistant Examiner-Cort Flint Attorney-Henry Stoltenberg [57] ABSTRACT A flywheel alternator with permanent magnet energiza- 9 Claims, 6 Drawing Figures PAIENIEDmzs ma FORWARD ATION to H f2 tl TRIGGER I l I I l l I I I l I WINDING VOLTAGE WI I 1 I SPEET 1 0F 4 lI-.'VEI\T(JRS. MAS E. S IFT IN J. B LEY x/34 ATTORNEY PAINIEDJux2s I973 SHEET 2 llf 4 1N VENTORS. THOMAS E. SWIFT ELWIN J. BRAYLEY ATTORNEY PAI-ENIEUJUNZB ms SHEH 3 BF 4 INVENTORS. S WI F T N10 wmo THOMAS E ELWIN J. BRAYLEY ATTOR N E Y 2 PATENIEUJUHZS I973 3 741 1 5 sum a nr 4 P w" H.

LQILLH' M i 8 1 x I M L r. fill H SH. W *iF i [y E W m: 4% I? 7 NWH INVENTURS. THOMAS E. SWIFT YL Y BY ELWIN J BRA E ATTORNEY CAPACITOR DISCHARGE IGNITION SYSTEM The invention contemplates the provision of a capacitor-discharge distributorless ignition system which can readily be adapted to several engines with a variable number of cylinders, without requiring extensive tooling changes for the manufacture thereof.

It is therefore a principal object of this invention to provide a capacitor-discharge distributorless ignition system for an engine with multiple cylinders.

It is a further object of this invention to provide an ignition system for a multiple cylinder engine which has maximum reliability.

It is further an object of this invention to provide an ignition system that will not allow the engine to run in reverse direction. (Important on two cycle engines) Other objects and advantages of this invention relating to the arrangement, operation and function of the related elements of the structure, to various details of construction, to combinations of parts and to economies of manufacture will be apparent to those skilled in the art upon consideration of the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

FIG. 1 is a bottom plan view of an alternator incorporating the invention.

FIG. 2 is a cross-sectional view taken along line 22 of FIG. 1.

FIG. 3 is a schematic diagram of connection of the invention for a two cylinder engine.

FIG. 4 is groups of curves showing the timing relations between the various aspects of the invention.

FIG. 5 is a schematic diagram of connection of a modification of the invention, and

FIG. 6 is a schematic diagram of connection of another modification of the invention.

Turning now to FIGS. 1 and 2 of the drawings, an engine (not shown) having a rotatable power shaft 10 is shown, usually journalled for vertical rotation in journal bearings 12 on the engine frame 13 such as found on large outboard marine engines on whose end a magnetic cup 14 is attached for rotation therewith in a wellknown manner. The downwardly projecting annular flange 16 is provided on its inner surface with a resilient magnetic member 18 which may be cemented in position or otherwise permanently attached thereto for rotation therewith. The magnetic member 18 is preferrably made of an elastomeric material, such as nitrile loaded with ferritic material which is capable of being permanently magnetized to form specific north and south poles at predetermined positions as shown to magnetically energize a stator member 20 made of magnetic laminations as is well known in the art. The stator member 20 is affixed in any suitable manner to the engine frame 13, so that its outwardly projecting poles 20A are held in fixed relation with the magnetic member 18 to cooperate therewith magnetically by a small air gap 22. There are 12 poles 20A provided in the device illustrated but it will be understood that this number may vary to suit required conditions. Each of the poles 20A is provided with a coil 24, which all cooperate together to provide the stator of a powergenerating alternator, except one or more coils W3 may be used for ignition purposes as will appear hereinafter. Rotation of the magnetic member 18 by the engine will excite the alternator coils 24 to provide an energy source for charging a battery (not shown) operating lights and the like. As shown 10 of the 12 coils shown, in FIG. 1 cooperate together for this purpose while the two remaining coils W3 provide a charging current for a capacitor-discharge ignition circuit as described hereinafter.

A second rotatable magnetic member 26, to excite stationary timing coils 28, is provided adjacent a central location concentric with the shaft 10 as best seen in FIG. 1. The magnetic member 26 consists of a permanent magnet 26A, cooperating with two

magnetic field members

26B and 26C which are semicircular in shape and are formed with a tapering cross-section with the massive portion being positioned adjacent the permanent magnet 26A while the smaller minimum portion is positioned diametrically opposite. The three elements are made as a sub-assembly by being cast in a zinc die casting which has a central aperture which is press fitted on on the reduced portion 30A of a rotatable cup 30 whose opposite enlarged end 30B terminates near the bottom of the main magnetic member 14. The cup 30 is mounted on the rotating shaft 10 for limited relative rotation to advance or retard the spark timing in accordance with speed of the engine by a centrifugal device 14A mounted inside of the cup 14. These centrifugal devices are well known in the art and will not be described in further detail. The magnetic cup 14 with its polarized magnetic member 18, the cup 30 and the second magnetic member 26 all rotate together with the rotating shaft 10, except that the relative angular position of the cup 14 and the second mag netic member 26 is capable of being varied to a limited degree by the action of the centrifugal device 14A to vary the ignition timing to the engine in accordance with the speed of the engine.

The stationary timing coils 28 are positioned in spaced relation in the cavities 40C of a non-magnetic circular die cast holder 40 in the form of a toroidal which is provided with a concentric flange 40A concentric with its center hole to enable the holder with its coils to be mounted on the lower side (right side, FIG. 2) of the stator member 20 by fitting the flange 40A into the central aperture 20C of the stator. These timing coils 28 and their magnetic cores 28C are mounted concentrically with the shaft 10 and cooperate magnetically with the periphery of the magnetic member 26 through a small air gap so that an electric current is generated in the coils when a main air gap 26g in the magnetic circuit of the permanent magnet 26A rotates past the magnetic cores 28C of the timing or trigger coils 28. The gap 26g is formed between the facing ends of the semicircular field members 268 and 26C and is preferrably formed by a kerf in the periphery of the magnetic member. Diametrically opposite, a second gap 26U is formed in the magnetic member 26 by another kerf, which however is not effective to create an electric current in the timing coils during rotation. Magnetic shields 28M are provided on the back side of the coils to prevent stray magnetic fields from the main alternator coils 24 or charging coils W3 from affecting the timing coils 28. It will be understood that the number of the coils 28 mounted in'the holder 40 correspond with the number of cylinders in the engine for which ignition is supplied. Three coils 28 are shown which is for use with a three cylinder engine.

A terminal block (not shown for clarity) may be mounted in cavity 40 for making convenient connections with outside circuits to the trigger coils 28. A schematic diagram of connections is shown in FlG. 3 which shows the relations of the charging coils W3 and the trigger coils 28 in a capacitor discharge ignition circuit for engines having a variable number of cylinders, which can be adapted to the various engines. The ignition system shown in FIG. 1, shows three trigger coils 28, while the diagram of connections shows a circuit for use with a two cylinder engine which can easily be expanded by adding another block B to the complete circuit assembly. Two blocks B1 and B2 are shown in FIG. 3 to which other blocks can be added to supply ignition to the cylinders of the engine. The block C shown above blocks B1 and B2 encompasses the capacitor charging arrangements and is common to all B blocks shown below.

The alternator coils 24 which are utilized to generate AC current for general power purposes such as lighting, battery-charging, and the like are electrically separate from the ignition circuits and will not be further described as they are well known in the art.

The capacitor charging arrangements as shown in block C for the capacitor-discharge ignition circuits as shown in blocks B1 and B2, is divided into two sections, a first section, for charging the capacitors at starting and initail idling of the engine which uses a low-voltage alternator winding 24 of relatively few turns, which has a dual function being also used for battery charging, and a second section for use beyond a predetermined speed of the engine which uses charging coil W3 having a larger number of turns. The charging coil W3 can be wound on pole 22 of the alternator stator or they can be divided and wound on two or more poles as required to attain the desired capacity or voltage. The capacitor C3 of blocks B1 and B2 must be charged by the circuit arrangements shown in block C so that when a timing pulse is generated in coils 28 (W1, W4, etc.) a thyristor SCR 1 (block Bl) will be tripped to a low resistance state, whereby the charge on capacitor C3 will discharge through the primary P of spark coil T2 and create a high voltage in its secondary S to fire spark plug X1 in the engine cylinder. In a similar manner coil 28 (W4) will fire the spark plug X2 in block B2 in its timed relation, all of which will be described in more detail hereinafter.

Special charging devices are necessary at starting of some engines in order to obtain the necessary voltages required to fire the spark plugs X1, X2, etc. in the engine cylinders. With the low rotative speeds of the magnetic member 14 at starting, insufficient voltage is generated in charging coils 24 (block C of FIG. 3) to charge the capacitors directly so that a step-up transformer T3 is required to raise the voltage to the required values. However, after the engine is started and the rotative speed increases to idling and higher speeds, the low-voltage charging coils 24 are heavily loaded by T3 due to its characteristics and it is therefore cut out from the alternator charging circuit and another highvoltage charging coil W3 more efficient for the purpose is utilized as will now be described.

Turning now to FIG. 3 Block C, it will he noted that alternator coils 24, the primary of transformer T3 and Thyristor SCR3 are in series circuit so that when thyristor SCR3 is in conductive state, the full output of alternator charging coils 24 will energize step-up transformer T3 whose secondary output is rectified by diodes CR13 and CR2 to charge capacitor C3 in block B1 preparatory to a timing pulse from timing coil W1 (28). The gate current for thyristor SCR3 is also supplied by charging coils 24 by flowing through resistor R5, resistor R11, and diode CR12 to the gate, which places the thyristor in conductance state. This is the condition of the charging circuit during starting of the engine.

After the engine starts and gate speed increases, the voltage generated by the alternator coils 24 increases, and also the voltage generated by the second charging coils W3. The increased voltage of coils 24 increases the charge on the capacitor C4 and when this charge voltage reaches the zener voltage of zener diode CR1], a sufficient gate voltage on thyristor SCR2 is impressed thereon, causing the thyristor SCR2 to become conductive, which shunts the gate voltage of the thyristor SCR3 so that thyristor SCR3 becomes non-conductive in the next half cycle of the alternating current which disconnects the primary of the transformer T3 from the alternator coils 24. The values of the components are selected so that this circuit is broken at a predetermined speed of rotation of the engine. As pointed out hereinbefore, this removes the excessive load from the alternator by disconnecting alternator coils 24 from transformer T3, but the coils 24 continue to charge the battery (not shown). The alternator can then create electrical energy for charging batteries and the like in its normal action as an alternator.

By the time the engine has reached the predetermined speed at which the primary of transformer T3 is disconnected from alternator coils 24, the second charging coil W3 is generating sufficient AC voltage, which when rectified by a full wave rectifier, consisting of diodes CR 14, CR 15, CR 16 and CR 17, charges the capacitors C3 in block B1, B2, etc. directly without the use of a step-up transformer. The charging coil W3 places a minimal load on the alternator when the engine is rotating at a speed above the predetermined speed. The

output terminals

41 and 42 of the full wave rectifier cooperating with the charging coil W3 are connected in parallel with the secondary of transformer T3 and diode CR 13 with terminal 41 being grounded as shown. Terminal 42 is connected to Buss l which supplies charging current for all of the capacitors C3 in block B1, B2, etc. from charging coils W3.

Terminals

42 and 41 are also connected in series with diode CR23, resistor R8, and capacitor C5, to provide a rectified current to energize transistors which form a part of the triggering circuits in block B1, B2, etc. as will appear hereinafter. Bus 2 is provided to carry this DC current to the various blocks as shown being connected to terminal 44 positioned between resistor R8 and capacitor C5. A zener diode CR20 is connected between

terminals

41 and 44 to control the maximum voltage at these points on Bus 2. In a similar manner zener diodes CR2] and CR22 are connected in series across

terminals

41 and 42 to control the maximum voltage on Bus 1. If desirable a single zener diode may be used at this point.

Terminal 42 and Bus 1 are also connected to resistor R9 and ignition switch I in series to ground. When the ignition switch I is in closed position, the charging circuits are grounded to stop the engine. In normal operation of the engine, ignition switch I is open as shown.

Turning now to the timing circuits for each of the blocks B1, B2, etc., which supply ignition pulses to the spark plugs X1, X2, etc. in the separate engine cylinders, only the circuits in block B1, will be described,

the remaining block B2, etc. being exactly the same in construction and operation. As has already been described, the charging devices in block C supply charging current to Bus 1 and also DC current to Bus 2 for the transistors, the two Busses l and 2 supply all of the blocks B1, B2, etc., with this energy.

In block B1 (and also the other block B2, etc.) Bus 1 is connected to diode CR2, which is connected in series circuit with main capacitor C3 and the primary P of spark coils T2 to ground via Bus 3. The secondary S of the spark coil T2 is connected to spark plug X1 which it fires in selected sequence for normal operation of the engine. The thyristor SCR1 controls the discharge of capacitor C3 through the primary P to create the high voltage in the secondary S to fire the spark plug X1. The thyristor SCRl is controlled by a circuit arrangement about to be described which is controlled by a broad voltage pulse from timing coil W1 (28) in the alternator. It will be understood that each cylinder of the engine is provided with these devices as found in the block B1, B2, etc. so that no conventional distributor is necessary.

The timing impulse which is applied to the gate of thyristor SCRl in block B1 is initiated by timing coil W1 (28) in the toroidal holder in which a broad pulse is produced by the relative rotation of the permanent magnet 26A and its

magnetic member

26B and 26C separated by the gap 26g and the coil W1 (28) as shown in FIG. 1. When rotation of the magnetic member is forward, the magnetic field created by the flux varies as shown in FIG. 4 with the maximum flux change occuring when gap 26g passes the coil W1 at time T3 to create a broad positive voltage pulse of low energy in the trigger winding or coil W1 which is applied to the base of transistor 01 to forward bias the transistor causing it to conduct collector current which flows to the primary 48 of transformer T1 to induce a voltage in a first secondary 50 connected to the base of the transistor 01 through resistor R1, the base being polarized to be regenerative so that it passes into its saturated state and creates a peaked pulse of short duration. The power to operate the transistor 01 is obtained from Bus 2 derived from block C as already described. This action causes a peaked pulse of current to flow through the primary of transformerTl, the duration of which is controlled and shortened by capacitor C2 and its interaction with the inductance of the transformer TI. This pulse induces a voltage in secondary 52 which is connected to the gate of thyristor SCRl, the pulse having sufficient energy to fire it to its low conductance state to discharge the capacitor C3 through the primary of high voltage transformer T2 to fire the spark plug X1 to perform the ignition function in the cylinder of the engine at its proper timed relation.

It is essential that the triggering pulse to the gate of the thyristor SCRl, shall not be longer than the duration of the ignition spark at the spark plug XI. The broad triggering pulse of low energy generated by winding W1 is applied to the transformer primary 48 of transformer T1 rather than directly to the gate of the thyristor SCRl to allow its energy to be augmented and its time duration shortened, which if too long could short out the charging winding W3 in block C. The capacitor C1 cooperating with base of the transistor 01 prevents parasitic oscillations in the trigger circuitry which could cause false firing of the ignition system.

Resistor R1 reduces the current flow in secondary 50 of the transformer T1 and also trigger winding W1. Resistor R3 connected across the capacitor C2 in circuit with Bus 2 and the primary 48 of the transformer T1 makes certain that capacitor C2 is discharged for each ignition cycle for the cylinder involved, particularly at high speeds. As mentioned hereinbefore diode CR2 between Bus 1 and capacitor C3 in each of the block B1, B2, etc. prevents the charges on the capacitors C3 from affecting the other capacitors C3 in the other blocks as for example discharging from one capacitor to another through Bus 1. The resistor R4 connected in parallel with the secondary 52 of the transformer T1 is to control the sensitivity of thyristor SCR] to better perform its function in the circuit.

Referring again to FIG. 4 the lower two curves shows the action of the trigger core flux threading coil or winding W1 (28) when the rotation of the engine occurs in a reverse direction. It will be noted that a negative voltage pulse is generated which reverse biases transistor Q1 which therefore does not respond and no ignition will occur to cause a continuation of the reverse rotation of the engine.

Referring now to FIG. 5, an alternate method of charging capacitors C3 from Bus 1A. Winding W12, W13, and W14 are wound on separate stator poles 20A as shown in FIG. 1 and are connected in series as shown. The three windings W12, W13, and W14 charge the capacitors C3 through diodes 0R6 and 0R7, 0R3, and 0R4, 0R8 and CR9, can have substituted for them single diodes if cost is not a desideratum. At the higher flywheel speeds coil W14 will charge capacitors C3 alone through diodes CR8 and 0R9.

With the windings W12, W13 and W14 in series, the voltage at point 61, the point interconnecting diodes 0R3 and 0R6 is the vector sum of the three charging voltages generated by the windings. From idle to midrange RPM of the engine, the voltage at point 61 is greater than the voltage across winding W14. As the engine increases in speed above the mid-range speed the voltage at point 61 is lower than the voltage across winding W14, which occurs due to an inductor Ll which is connected in parallel with diode 0R5 and capacitor O4. Diode 0R5 is in series circuit with diodes CR3 and 0R4, all three diodes being in parallel with windings W12, W13 and W14, one end being connected to point 61, while the other end is grounded. Capacitor O4 limits the high frequency harmonics of the inductor Ll, while diode 0R5 shorts the positive induced voltages, which results from the collapse of the magnetic field of the inductor L1 generated by the negative excursion of voltage from the charging windings.

The inductor Ll has a further function in the circuit to suppress the inverse generated voltage of windings W12, W13 and W14, by imposing a lagging power factor load on each via diodes 0R3 and 0R4. if the inverse voltages were left in open circuit they would be high enough to endanger the insulation of the system and could reach two thousand volts. The inductor L1 is designed with selected values to limit these inverse voltages generated by the windings W12, W13 and W14 to approximately 600 volts.

At the higher engine speeds, as pointed out before, the charging of capacitors C3 is provided by winding W14, whose voltage at these speeds is' greater than the voltage at point 61. This is due to the fact that the inductor Ll imposes a larger lagging power factor load to the vector sum of the voltages on the three series windings W12,'W13 and W14 than it does on anyof the individual windings, especially winding W14. The inverse voltage generated in winding W14 is limited by the heavy load imposed by charging the capacitors C3 during the positive voltage excursion of the generated voltage, and also by the lagging power factor loading by inductor L1 during the negative or inverse excursion of winding W12 and W13. The use of the inductor Ll for this purpose reduces the power dissipation to a relatively low wattage as compared to the wattage dissipated, if a resistive loading were utilized. In the circuit capacitor limits the high frequency emanations from the circuit, generated by the firing of the SCRs.

It will be appreciated by a man skilled in the art that the ignition circuits shown in FIGS. 3 and 5 can be modified to use a single capacitor C3 to energize the primaries of the separate high tension ignition coils for the separate cylinders. Such a circuit is shown in FIG. 6 where capacitor C3A serves the high tension ignition coils for all cylinders. The equivalent circuit points 42 and 44 of FIG. 3 are indicated in FIG. 5 as 42A and 44A, and as 428 and 448 in FIG. 6 It will also be noted in FIG. 6 that the Thyristor SCRIA controlling the discharge of the capacitor C3A into the primaries of the high tension coils is connected directly in series with the individual primaries.

We claim:

1. In a capacitor-discharge ignition system for a multiple-cylinder internal combustion engine, a part rotated by the engine to create a varying magnetic field, an ignition circuit for each cylinder including a capacitor, a thyristor, a high-voltage coil and a spark plug fired by the high-voltage coil, a low-speed charging winding activated by the varying magnetic field for the capacitor with a control, a high-speed charging winding activated by the varying magnetic field for the capacitor in parallel therewith, said control changing the effect of the low-speed charging winding at a predetermined speed of the engine, said control including a step-up transformer having its secondary operatively connected to said capacitor and its primary connected in series to said low speed charging winding through an electronic switch, said switch being biased in its conductive state when said engine speed is below said predetermined speed, and a voltage responsive device operatively connected to said low speed winding and said electronic switch and effective to cause said switch to assume its non-conductive state to open circuit said primary of said' step-up transformer when said engine speed reaches said predetermined speed, thereby effectively changing the effect of said low-speed charging winding, a timing gate control means for the thyristor to discharge the capacitor through the primary of the high-voltage coil to cause firing of the spark plug, the timing gate control means including a timing coil to create a timing pulse activated by a second varying magnetic field cooperating with the rotating part and an amplifier for increasing the energy of the timing pulse and to peak the same to fire the thyristor.

2. The ignition circuit defined in claim 1 further characterized by the amplifier including a regenerative circuit which augments the energy of the timing pulse and controls its time duration.

3. The ignition circuit defined in claim 1 further characterized by the amplifier including a transformer and a transistor which obtains operating energy from the charging coils.

4. The ignition circuit defined in claim 3 wherein the base of the transistor is in circuit with a secondary of the transformer and a capacitor to create a regenerative action on the transistor.

5. The capacitor discharge ignition circuit of claim 1 wherein said voltage responsive device includes a zener diode and a second controlled conduction device operatively connected to said low speed charging winding and to the control electrode of said electronic switch such that the output voltage from said low speed winding, when said engine speed reaches said predetermined value, is effective to cause said second controlled conduction device to conduct, thereby shunting the control electrode of said electronic switch to cause it to assume its non-conductive state to open circuit said primary of said step-up transformer.

6. The capacitor discharge ignition circuit of claim 1 wherein said low speed charging winding is also operatively connected to a battery in parallel relation to said capacitor.

7. In a capacitor discharge ignition circuit including a capacitor and a controlled conduction device operatively connected to a spark device and a trigger device responsive to engine speed operatively connected to said controlled discharge device to cause said controlled conduction device to discharge said capacitor to said spark device on timed relation to engine speed, the improvement comprising a first and a second charging winding operatively connected to said capacitor, said first charging winding having a relatively low voltage output connected to said capacitor through a step-up transformer and said second charging winding having a relatively high voltage output connected directly to said capacitor, and means for effectively preventing said first charging winding from charging said capacitor at speeds above a predetermined engine speed, said last name means including an electronic switch operatively connected in circuit with said first charging winding and the primary of said step-up transformer and biased in its conductive state when said engine speed is below said predetermined engine speed, a voltage responsive device operatively connected to said first charging winding and said electronic switch and effective to cause said switch to assume its non-conductive state to open circuit said primary of said step-up transformer when said engine reaches said predetermined speed, thereby effectively preventing said first charging winding from charging said capacitor at speeds above said predetermined engine speed.

8. The capacitor discharge ignition circuit of claim 7 wherein said voltage responsive device includes a zener diode and a second controlled conduction device operatively connected to said first charging winding and to the control electrode of said electronic switch such that the output voltage from said first winding, when said engine speed reaches said predetermined value, is effective to cause said second controlled conduction device to conduct, thereby shunting the control electrode of said electronic switch to cause it to assume its nonconductive state to open circuit said primary of said step-up transformer.

9. The capacitor discharge ignition circuit of claim 7 wherein said first charging winding is alsooperatively connected to a battery in parallel relation to said capacitor.

i t 1k

Claims

1. In a capacitor-discharge ignition system for a multiplecylinder internal combustion engine, a part rotated by the engine to create a varying magnetic field, an ignition circuit for each cylinder including a capacitor, a thyristor, a high-voltage coil and a spark plug fired by the high-voltage coil, a low-speed charging winding activated by the varying magnetic field for the capacitor with a control, a high-speed charging winding activated by the varying magnetic field for the capacitor in parallel therewith, said control changing the effect of the low-speed charging winding at a predetermined speed of the engine, said control including a step-up transformer having its secondary operatively connected to said capacitor and its primary connected in series to said low speed charging winding through an electronic switch, said switch being biased in its conductive state when said engine speed is below said predetermined speed, and a voltage responsive device operatively connected to said low speed winding and said electronic switch and effective to cause said switch to assume its non-conductive state to open circuit said primary of said step-up transformer when said engine speed reaches said predetermined speed, thereby effectively changing the effect of said low-speed charging winding, a timing gate control means for the thyristor to discharge the capacitor through the primary of the high-voltage coil to cause firing of the spark plug, the timing gate control means including a timing coil to create a timing pulse activated by a second varying magnetic field cooperating with the rotating part and an amplifier for increasing the energy of the timing pulse and to peak the same to fire the thyristor.

8. The capacitor discharge ignition circuit of claim 7 wherein said voltage responsive device includes a zener diode and a second controlled conduction device operatively connected to said first charging winding and to the control electrode of said electronic switch such that the output voltage from said first winding, when said engine speed reaches said predetermined value, is effective to cause said second controlled conduction device to conduct, thereby shunting the control electrode of said electronic switch to cause it to assume its non-conductive state to open circuit said primary of said step-up transformer.

9. The capacitor discharge ignition circuit of claim 7 wherein said first charging winding is also operatively connected to a battery in parallel relation to said capacitor.