US3866589A

US3866589A - Semiconductor controlled magneto ignition system for internal combustion engines

Info

Publication number: US3866589A
Application number: US330742A
Authority: US
Inventors: Georg Haubner; Peter Schmaldienst
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1972-03-10
Filing date: 1973-02-08
Publication date: 1975-02-18
Anticipated expiration: 1992-02-18
Also published as: SE378442B; IT981261B; JPS49626A; DE2211575A1; DE2211575C2; ES412476A1

Abstract

A magneto generator is driven by the engine and provides output energy which varies with change in engine speed. The output energy is applied to an energy storage device, typically a capacitor, which is charged and, when a semiconductor switching element is rendered conductive, the stored energy is used to generate the spark of the spark plug. In order to provide for spark-advance as the speed of the engine increases, the magneto generator is wound to provide two half waves of output which are sequential, in time, for example by having two oppositely phased windings, or a center tapped winding, from which half waves are obtained, the first being of lesser amplitude than the second. During slow speed operation, only the second half wave will trigger the semiconductor to provide a spark discharge; upon high-speed operation, sufficient amplitude is derived from the first winding so that the spark will be triggered earlier, thus providing for spark-advance upon high-speed engine operation.

Description

tjnited States Patent 1191 1111 3,866,589

Hauhner et al. 451 F 13, 19

[ SEMICONDUCTOR CONTROLLED MAGNETO IGNITION SYSTEM FOR Primary ExaminerCharles J. Myhre INTERNAL COMBUSTION ENGINES Assistant Examiner-Ronald B. Cox

[ Inventors: Georg Hammer, g; Peter Attorney, Agent, or Firm-Flynn & Frishauf Schmaldienst, Nurnberg, both of Germany [57] ABSTRACT [73] Assigneez Robert Bosch GmbH magneto generator is driven hy the engine and pro Gerligen-Schillerhohl, Germany vides output energy which varies with change in engme speed. The output energy is applied to an energy Flledi 1973 storage device, typically a capacitor, which is charged [21] AppL NOJ 330,742 and, when a semiconductor switching element is rendered conductive, the stored energy is used to generate the spark of the spark plug. In order to provide for Foreign Application Priority Data spark-advance as the speed of the engine increases, Mar. 10, 1972 Germany 2211575 the magneto generator is wound to provide two half waves of output which are sequential, in time, for ex- [52] U.S. Cl. 123/148 MC, 123/118, 123/148 E ample by having two oppositely phased windings, or a [5 1] Int. Cl. F02p l/00 center tapped winding, from which half waves are ob- [58] Field of Search 123/148 MCD, 148 E, l 18 tained, the first being of lesser amplitude than the second. During slow speed operation, only the second [56] References Cited half wave will trigger the semiconductor to provide a UNITED STATES PATENTS spark discharge; upon high-speed operation, sufficient 3 367 314 9/1965 Hirosawa et al. 123/148 MCD amplitud? is f from the .first Winding h the 3:553:529 1/1971 Strelow 123/148 MCD Spark be "lggered earner, thus Pmvldmg for 3,630,185 12/1971 Struber 123/148 MCD Spark-advance upon high-Speed engine Operation- 7 4, 00 12 1972 Weseme er. 123 148 MCD 31728 155 10/1973 1mh6f..... 123/148 MCD 17 Clams 5 Drawmg F'gures PATENTED FEB] 8197? SWITCH ENERiGIE 23 MEANS STORAGE MEANS 1 SEMICONDUCTOR CONTROLLED MAGNETO IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINES The present invention relates to an ignition system for internal combustion engines and more particularly to a semiconductor controlled magneto ignition system in which sparking energy derived from the magneto generator is dependent on speed of the engine to which it is coupled.

Ignition systems utilizing magneto generators have been proposed, in which the magneto generator is connected over diodes to a capacitor serving as an energy storage device. To reduce air pollution from the exhaust of the internal combustion engine, it is desirable that the engine operate with retarded spark when running at low speeds. During high-speed operation, however, and to obtain good operating efficiency, the spark should be advanced so that the ignition timing is in advance of dead-center position of the piston of the engine.

Various solutions have been proposed in order to obtain change in ignition timing with speed when using magneto generators and semiconductor controlled ignition systems, that is, without mechanical change of ignition control. In one such system, an additional magnetic transducer is provided, which has two different windings, wound in opposite directions. The windings are connected in parallel over a diode. The magnetic pulse source is connected to the control electrode of a thyristor (SCR) connected in the discharge circuit of the capacitor. The positive voltage half wave of the smaller transducer winding occurs in advance of the positive half wave of the larger transducer winding. In a lower region of engine speed, the thyristor is fired by the voltage half wave of the larger transducer winding, and in upper speed ranges, the voltage of the smaller transducer winding is sufficient. Thus, the ignition tim ing jumps from retarded spark to advanced spark as the engine speed exceeds a certain value.

A further solution has been proposed in which a sudden change of the ignition timing is obtained by a pair of transducers located in circumferential direction of the magneto generator, the transducers providing control pulses of different amplitudes.

The solutions referred to have the disadvantage that special pulse sources are necessary to control the electronic switching elements, typically SCRs, which have several windings, or that the transducers must be located on the magneto generator in pairs. Such ignition systems therefore are expensive in manufacture and, due to their large space requirements, frequently cannot be located in small internal combustion engines.

It is an object of the present invention to provide an ignition system which permits control of electronic circuit elements without additional pulse sources, such that the ignition timing can be changed upon change in speed of the engine, within predetermined limits.

SUBJECT MATTER OF THE PRESENT INVENTION Briefly, the magneto generator provides during each rotation two sequentially occurring voltage half waves to the energy source; to change the ignition timing, the first half wave has a smaller amplitude than the second. The electronic circuit element has a control electrode which is connected to the energy storage device, preferably over a voltage-dependent element such as, for I example, a Zener diode, to control the electronic switching element when the energy storage device reaches a certain stored voltage.

In a preferred form of the invention, the energy storage device comprises a capacitor which is connected to the primary winding of an ignition coil, in series, the secondary winding of which is connected to the spark plug. The electronic circuit element is connected in parallel to the capacitor and to the ignition coil, and is a thyristor, for example an SCR. The voltages supplied by the magneto generator are applied over diodes to the capacitor, as alternating voltages which are in phase opposition and which have different amplitudes. It is also possible to provide a magneto which provides only a single alternating voltage of which the first positive voltage half wave has a smaller amplitude than the second negative voltage half wave.

The invention will be described by way of example with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic diagram of a magneto generator supplying an ignition system in which the ignition timing is speed-dependent;

FIG. 2 is a detailed circuit diagram of a capacitor ignition system supplied from a pair of supply windings;

FIG. 3 is a timing diagram of voltages in the supply windings of the generator of FIG. 1;

FIG. 4 is a timing diagram showing voltage on the capacitor of an ignition system of FIG. 2; and

FIG. 5 is a fragmentary view illustrating a modification of the circuit including the magneto generator to supply a capacitor discharge system.

A magneto generator for a one-cylinder two-stroke internal combustion engine 10 is preferably secured to the fly-wheel of the internal combustion engine. It includes a permanent magnet 12, for example cast into the fly-wheel, which has a pair of

pole shoes

13, 14 located at the circumference of the flywheel. The housing of the internal combustion engine not shown has an armature 15 secured thereto which includes a U- shaped iron core 16, having

pole shoes

16a, 16a extending from the outside towards the circumference of fly-wheel ll.

Pole shoes

13 and 14 of the permanent magnet 12 pass once beneath

pole shoes

16a, 16a of core 16 for each revolution of the flywheel 11. Core 16 has two

windings

17, 18 placed thereon which are each connected over lines 19, 211) with the electronic circuit 21 of the ignition system. The electronic circuit 21 is connected to an energy storage device 22 which, in turn, is connected at its output to a spark plug schematically shown at 23.

The detailed circuit is seen in FIG. 2, in which the same reference numerals have been used to indicate the same elements. Supplying windings l7, 18 of the magneto generator 10 are connected to be oppositely phased. One of their terminals is jointly connected over a tap line 24 to ground or chassis. The free ends of windings l7 and 18 are connected to

supply lines

19 and 20 and then to diodes 25, 26 connected in the electronic unit 21. The diodes, which are equally poled, are connected over a line 31 with the energy storage and ignition circuit 22. The energy storage element itself is a capacitor 27, connected to the primary winding 28a of ignition coil 28, in series therewith. Secondary winding 28b of ignition coil 28 is connected to spark plug 23. A diode 29 is connected in parallel to primary 28a of ignition transformer 28. The anode of diode 29 is connected to capacitor 27 and the cathode to chassis. The electronic switching device 21 includes a thyristor 30, the anode of which is connected to line 31 and hence to capacitor 27. The thyristor 30 is in parallel to capacitor 27 and the primary winding 28a of ignition coil 28. The gate electrode 30a of thyristor 30 is connected to line 31, and hence to the capacitor 27 over a voltage-dependent circuit element, such as a Zener diode 33 in series with a resistor 34.

Operation (with reference to FIGS. 3 and 4): Upon rotation of fly-wheel l1,

supply windings

17, 18 will have oppositely phased voltages U U induced therein see FIG. 3. Voltage U has a smaller amplitude than voltage U due to the lower number of winding turns of winding 17 with respect'to the number of turns of winding 18. Capacitor 27 is charged by the positive half waves of voltages U U that is, the half waves which are passed by

diodes

25 and 26. The smaller positive voltage half wave U is applied to capacitor 27 immediately in advance of the larger positive half wave U to pre-charge the capacitor.

At low speed the voltage generated by supply winding 17, that is, the winding with the lesser number of turns, derived from the capacitor 27 is less than the switching or threshold or triggering voltage necessary to render thyristor 30 conductive. The voltage is indicated as voltage U and varies as shown by the solid curve of FIG. 4. The Zener voltage U; is also shown in FIG. 4. Only the subsequently occurring larger positive voltage half wave U will exceed Zener voltage U Thus, only when the positive half wave U is applied to the capacitor so that the capacitor voltage U, will be in excess of the Zener voltage U will Zener diode 33 become conductive. which will occur at the ignition timing point Z Thyristor 30 will thus switch into conductive state, and capacitor-27 can discharge over thyristor 30 and primary 28a of ignition coil 28. Secondary 28b of coil 28 will have the ignition voltage induced therein which causes a spark at spark plug 23. After capacitor 27 has discharged, thyristor 30 will again revert to blocking conditions, and the capacitor 27 will be recharged upon further rotation of fly-wheel 11 by the positive voltage half waves of voltages U U,,,. Ignition will occur cyclically upon each full rotation of flywheel 11. Upon charge of capacitor 27, the primary 28a of the transformer 28 is bridged by diode 29 so that high voltages in the secondary 28b of the ignition transformer 28 are suppressed. This reliably eliminates misfires of the spark plug 23.

Upon increasing speed ofthe internal combustion engine, fly-wheel 11 will turn faster and the voltages U and U induced in

supply windings

17, 18 will increase. At a certain speed, which may be termed the critical speed, the ignition timing will suddenly change to spark-advance. At this critical speed, and above this critical speed, the positive half wave causipgvoltage U from supply winding 17, that is, the winding with the lesser number of turns, will have a voltage induced which is sufficient to charge capacitor 27 to a value at which the capacitor voltage U, is greater than the Zener voltage U; of Zener diode 33. Thyristor 30 will thus be triggered into conductive state already by the voltage derived from coil 17. This voltage is shown in FIG. 4 in the chain-dotted graph.

The ignition timing instantjumps by an ignition angle A41, which depends on the distance of the two positive half waves of voltages U U from each other. Distance (in time) is given by the dimensions of armature 15 and pole faces 13 and 14 of permanent magnet 12. It can be changed by changing the physical dimensions of the magneto system.

The speed at which the ignition timing changes from delayed spark to advanced spark can be selected by suitable dimensioning of the

supply windings

17, 18. For example, the arrangement can be so made that the internal combustion engine operates below critical speed with retarded spark to provide for minimum polluting exhaust gases, while operating with maximum power and efficiency above critical speed, at which time the spark is advanced.

FIG. 5 illustrates a magneto generator in which the two supply windings are parts of a single coil 32 which has a tap 24a connected to chassis. The free ends of coil 32 are connected over

lines

19, 20 and over a

diode

25, 26, each, to line 31, and hence to capacitor 27. Both

diodes

25, 26 are formed as one integral diode unit, having two anode terminals and a single cathode connection. The tap 24a, as well as the free end of the lower part 32a of coil 32 are connected to chassis over diodes 36, 37 which are integrated into a diode array, or diode unit 38. Diode unit 38 is reversely poled with respect to diode unit 35, that is, it has two cathode terminals and a single anode terminal which is connected to chassis. Line 31 connecting to capacitor 27 is connected to the control gate electrode 30a of thyristor 30 over a voltage dependent resistor 39 (VDR). The cathode of thyristor 30 is connected to chassis.

OPERATION Essentially, the operation is similar to that explained in connection with the system of FIG. 2. The

diode units

35, 38 effect connection of the winding portions 32a and 32b of coil 32 in such a manner that the induced voltages in the first half period are connected in phase opposition. The positive half wave induced in coil portion 320 is conducted over diode 26 and line 31 to capacitor 27, the circuit being closed to chassis over diode 36. Capacitor 27 is thus charged to a charge value U, by the half wave derived from winding portion 32a in the lower speed range of operation of the engine. This voltage U, is below the necessary voltage to fire thyristor 30. In the second period half, the voltages in windings 32a and 32b are added by the arrangement of the

diode units

35 and 38, so that the full coil voltage of coil 32 is connected over diode 25 and line 31 to capacitor 27, the circuit being completed to chassis over diode 37. The embodiment of FIG. 5 permits construction of a coil 32 having the same number of windings as the coil 18 in FIGS. 1 and 2. Winding 17 is no longer necessary since the lower voltage U (FIG. 3) is tapped off coil 32, as a portion of the larger voltage U,,,. The voltage dependent resistor 39 is so dimensioned that only when the voltage U, appears at capacitor 27, the thyristor 30 will have sufficient voltage applied thereto so that the thyristor will fire. The coil 32 provides that in the lower speed ranges, the thyristor is switched only by the second voltage half wave; in higher speed ranges, it is already switched at the first voltage half wave.

Charging capacitor 27 requires a certain period of time, which depends on the ohmic resistance in the charging circuit. It is therefore highly dependent on the resistance of windings 17, 18 (or coil 32, respectively). Control of this resistance can be used, in accordance with a feature of the invention, to control the resistor 30 to additionally have a governing function to limit the upper speed of the engine. The resistance in the charging circuit is then so taken that capacitor 27 is no longer charged to the necessary voltage when maximum speed is reached. Thus, at any revolution of flywheel 11, the voltage necessary to switch thyristor 30 is no longer obtained since the capacitor 27 will no longer be charged to this value. As a result, there will be misfires, that is, the spark plug will fail to fire from time to time. Firing failures are much less dangerous than complete disconnection of the ignition system. The ohmic resistance in the charge circuit of the ignition system can be regulated or set readily by a resistor, for example by a resistor 40 shown in dashed lines and connected in series with diode 29, FIG. 2.

The present invention is not restricted to the examples, since various specific features may be omitted, or exchanged with respect to each other. For example, Zener diode 33 can be replaced by any electronic element which provides a voltage dependent control signal.

The thyristor can be self-controlling, that is, without having a voltage dependent element connected to the control electrode; it is then only necessary to connect the control or gate electrode 30a over a resistor with its cathode connection, so that the thyristor will remain reliably blocked. The energy storage device may be capacitative, as shown, or may be inductive. it is only necessary that the voltage of the magneto generator have two subsequently occurring half waves supplying electric energy to be stored, the first half wave being smaller than the second voltage half wave, and so dimensioned that in low speed regions the lower or smaller voltage half wave is insufficient to switch over thyristor 30 or some other electronic switching element. The voltage of the magneto generator can be also an alternating voltage having a smaller positive and a larger negative half wave, which is applied to the energy storage device over a full wave rectifier. Such a! ternating voltage can readily be generated by shunting a portion of coil 32 of the magneto generator by a diode and a protective resistor.

Various other changes and modifications may be made within the inventive concept.

We claim:

1. Semiconductor controlled magneto ignition system for internal combustion engines having a magneto generator driven by the engine and providing output energy varying with speed of the engine,

an energy storage device (22, 27) connected to the magneto generator (10) to provide energy to a spark plug of the engine,

and an electrical control circuit including a controlled switching element to control delivery of the stored energy to the spark plug at a proper ignition timing;

wherein the magneto generator (10) is wound to provide, for each revolution thereof, at least two sequential voltage half waves (U um) 10 the energy storage device (22, 27), the first (U,,) of the sequential half waves having a lesser amplitude than the second (U wherein said electrical control circuit is arranged to respond to said sequential voltage half waves;

wherein, further, the control terminal (30a) of said switching element (30) is connected to the storage device (22, 27) and is provided by said control circuit with a predetermined switching control voltage threshold level (U at which switching of the switching element into conductive state takes place, when the storage device, (U reaches said threshold level so that, during; low-speed operation, only the second, larger voltage half wave (U will have sufficient amplitude to store sufficient energy in the enery storage device to reach said threshold level and, upon increase in speed of the engine, the first voltage half wave (U will have sufficient amplitude therefor and thus cause earlier conduction of the controlled switch and hence advance of spark timing,

and wherein the resistance of the circuit, to which the energy storage device (22, 27) is connected for charging said energy storage device, has a value high enough to prevent charging of the energy storage device to a level at which its voltage (U reaches the threshold level of the controlled switching element (30) when the engine operates at a speed in excess of a predetermined maximum speed and thus to effect inherent governor action.

2. System according to claim 1,. further comprising a resistor (40) in circuit with the energy storage device and dimensioned to introduce sufficient resistance to the circuit so that the circuit will have said resistance to effect governor action.

3. System according to claim 1, wherein the energy storage device comprises a capacitor (27), and an ignition coil (28) is provided having its primary (28a) connected in series with the capacitor and its secondary (28b) to the spark plug.

4. System according to claim 1, wherein the controllable switching element comprises a thyristor (30) connected in parallel to the series connection of the capacitor (27) and the ignition coil (28).

5. System according to claim 1, wherein the magneto generator (10) has an armature (1.6) provided with two oppositely phased windings (l7, 18) located on the armature each having one end terminal connected by a separate circuit path to the energy storage device (22, 27 device and both having in common a terminal connected to chassis of the engine, or ground.

6. System according to claim 5, wherein the energy storage device is a capacitor (27) and diodes (25, 26) are provided respectively connecting the non-common end terminals of the oppositely phased windings (17, 18) to the capacitor.

7. System according to claim 6 wherein the diodes are formed as a single diode unit (35) having one commonly poled integrated terminal, and two separate oppositely poled terminals, the separate terminals being connected to said non-common end terminals of the windings.

8. System according to claim 7, wherein the separate oppositely poled diode terminals are the anodes, said commonly poled terminal is the cathode, and the cathode is connected to the capacitor (27).

9. System according to claim 5, wherein the two windings (32a, 32b) are formed :as a single coil (32) having a tap points (24a), the tap point being connected to the chassis of the engine, or ground.

l0. Semiconductor controlled magneto ignition system for an internal combustion engine having an energy storage means (22, 27) for providing collected energy to a spark plug of the engine;

a magneto generator driven by the engine and providing output energy varying with speed of the engine, said magneto generator having an armature (16) provided with two oppositely phased windings (17, 18) located on the armature each having one end terminal connected by a separate circuit path, including in each case a diode (25, 26) to the energy storage device (22, 27) and both windings having a common terminal;

a second set of diodes (3, 6, 37) connected respectively between said common terminal and the chassis of the engine and between the non-common end terminal of one of said windings and the chassis of the engine,

and an electrical control circuit including a controlled switching element (30) to control delivery of the stored energy to the spark plug at a proper ignition timing;

said windings being proportioned to provide, for each revolution of said magneto generator, at least two sequential voltage half waves (U U,,,) to the energy storage device (22, 27), the first (U of the sequential half waves having a lesser amplitude than the second (U and wherein said electrical control circuit is arranged to respond to said sequential voltage half waves;

wherein, further, the control terminal (30a) of said switching element is connected to the storage device (22, 27) and is provided by said control circuit with a predetermined switching control voltage threshold level (U at which switching of the switching element into conductive state takes place, when the storage device voltage (U,) reaches said threshold level so that, during lowspeed operation, only the second, larger voltage half wave (U will have sufficient amplitude to store sufficient energy in the energy storage device to reach said threshold level and, upon increase in speed of the engine, the first voltage half wave (U,,) will have sufficient amplitude therefor and thus cause earlier conduction of the controlled switch and hence advance of spark timing.

11. System according to claim 10, wherein the energy storage device is a capacator and wherein the two windings (32a, 32b) are formed as a single coil (32) having at that point (24a) serving as the common terminal of said windings.

12. System according to claim 10 wherein said diodes connected to the engine chassis and likewise the diodes in said separate paths to said storage device are pairs formed as a single diode unit having one commonly poled integrated terminal and two separate, oppositely poled terminals, the commonly poled integrated terminals being respectively connected to the engine chassis and to said storage device.

13. System according to claim 12, wherein the separate terminals are the cathodes and the common terminal is the anode, the anode being connected to chassis or ground.

14. System according to claim I, further comprising a voltage-dependent circuit element (33, 39) connecting the voltage (U on the storage device (22, 27) to the switching element (30) the voltage-dependent circuit element having a predetermined voltage transfer level, the voltage threshold level required to switch said switching element (30) being selected to be higher than the first voltage half wave (U derived from the generator (10) when the generator is driven by the engine in a low-speed range, said voltage transfer level of the voltage-dependent circuit element being matched to the switching threshold level of the switching element and being at least as great as said threshold level, and being higher than the first voltage half wave (U when the generator is driven by the engine in a low-speed range to reliably prevent triggering of said switching element by said first voltage half wave (U when the engine is operating in the low-speed range.

15. System according to claim 14, wherein the voltage-dependent circuit element comprises a Zener diode (33).

16. System according to claim 15, further comprising a resistor (34) in series with the Zener diode.

17. System according to claim 14, wherein the voltage-dependent circuit element comprises a voltagedependent resistor (39).

Claims

1. Semiconductor controlled magneto ignition system for internal combustion engines having a magneto generator (10) driven by the engine and providing output energy varying with speed of the engine, an energy storage device (22, 27) connected to the magneto generator (10) to provide energy to a spark plug of the engine, and an electrical control circuit including a controlled switching element (30) to control delivery of the stored energy to the spark plug at a proper ignition timing; wherein the magneto generator (10) is wound to provide, for each revolution thereof, at least two sequential voltage half waves (U17, U18) to the energy storage device (22, 27), the first (U17) of the sequential half waves having a lesser amplitude than the second (U18), wherein said electrical control circuit is arranged to respond to said sequential voltage half waves; wherein, further, the control terminal (30a) of said switching element (30) is connected to the storage device (22, 27) and is provided by said control circuit with a predetermined switching control voltage threshold level (UZ) at which switching of the switching element into conductive state takes place, when the storage device, (Ue) reaches said threshold level so that, during low-speed operation, only the second, larger voltage half wave (U18) will have sufficient amplitude to store sufficient energy in the enery storage device to reach said threshold level and, upon increase in speed of the engine, the first voltage half wave (U17) will have sufficient amplitude therefor and thus cause earlier conduction of the controlled switch and hence advance of spark timing, and wherein the resistance of the circuit, to which the energy storage device (22, 27) is connected for charging said energy storage device, has a value high enough to prevent charging of the energy storage device to a level at which its voltage (Uc) reaches the threshold level of the controlled switching element (30) when the engine operates at a speed in excess of a predetermined maximum speed and thus to effect inherent governor action.

2. System according to claim 1, further comprising a resistor (40) in circuit with the energy storage device and dimensioned to introduce sufficient resistance to the circuit so that the circuit will have said resistance to effect governor action.

5. System according to claim 1, wherein the magneto generator (10) has an armature (16) provided with two oppositely phased windings (17, 18) located on the armature each having one end terminal connected by a separate circuit path to the energy storage device (22, 27), device and both having in common a terminal connected to chassis of the engine, or ground.

7. System according to claim 6, wherein the diodes are formed as a single diode unit (35) having one commonly poled integrated terminal, and two separate oppositely poled terminals, the separate terminals being connected to said non-common end terminals of the windings.

9. System according to claim 5, wherein the two windings (32a, 32b) are formed as a single coil (32) having a tap points (24a), the tap point being connected to the chassis of the engine, or ground.

10. Semiconductor controlled magneto ignition system for an internal combustion engine having an energy storage means (22, 27) for providing collected energy to a spark plug of the engine; a magneto generator driven by the engine and providing output energy varying with speed of the engine, said magneto generator having an armature (16) provided with two oppositely phased windings (17, 18) located on the armature each having one end terminal connected by a separate circuit path, including in each case a diode (25, 26) to the energy storage device (22, 27) and both windings having a common terminal; a second set of diodes (3, 6, 37) connected respectively between said common terminal and the chassis of the engine and between the non-common end terminal of one of said windings and the chassis of the engine, and an electrical control circuit including a controlled switching element (30) to control delivery of the stored energy to the spark plug at a proper ignition timing; said windings being proportioned to provide, for each revolution of said magneto generator, at least two sequential voltage half waves (U17, U18) to the energy storage device (22, 27), the first (U17) of the sequential half waves having a lesser amplitude than the second (U18); and wherein said electrical control circuit is arranged to respond to said sequential voltage half waves; wherein, further, the control terminal (30a) of said switching element is connected to the storage device (22, 27) and is provided by said control circuit with a predeTermined switching control voltage threshold level (UZ) at which switching of the switching element into conductive state takes place, when the storage device voltage (Uc) reaches said threshold level so that, during low-speed operation, only the second, larger voltage half wave (U18) will have sufficient amplitude to store sufficient energy in the energy storage device to reach said threshold level and, upon increase in speed of the engine, the first voltage half wave (U17) will have sufficient amplitude therefor and thus cause earlier conduction of the controlled switch and hence advance of spark timing.

14. System according to claim 1, further comprising a voltage-dependent circuit element (33, 39) connecting the voltage (Uc) on the storage device (22, 27) to the switching element (30) the voltage-dependent circuit element having a predetermined voltage transfer level, the voltage threshold level required to switch said switching element (30) being selected to be higher than the first voltage half wave (U17) derived from the generator (10) when the generator is driven by the engine in a low-speed range, said voltage transfer level of the voltage-dependent circuit element being matched to the switching threshold level of the switching element and being at least as great as said threshold level, and being higher than the first voltage half wave (U17) when the generator is driven by the engine in a low-speed range to reliably prevent triggering of said switching element by said first voltage half wave (U17) when the engine is operating in the low-speed range.

17. System according to claim 14, wherein the voltage-dependent circuit element comprises a voltage-dependent resistor (39).