Ignition System For Multicylinder Internal Combustion Engine

Abstract

An ignition system for a multicylinder internal combustion engine comprising an ignition power source, a capacitor, a pair of charging circuits, a pair of discharging circuits, a pair of ignition coils each having a primary and a secondary winding, and at least one ignition plug connected to each of the secondary windings of the ignition coils. In the system, the charging circuits are arranged to charge the capacitor in directions opposite to each other, and the primary windings of the ignition coils are disposed in such circuit portions of the discharging circuits where these circuits do not overlap each other.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a capacitor discharge type ignition system for use in multicylinder internal combustion engines such as two-cycle two cylinder engines and four-cycle four cylinder engines.

2. Description of the Prior Art

In known ignition systems of this kind, it is customary to provide a power source for charging a single capacitor and to connect a plurality of series circuits each including a series connecton of a primary winding of an ignition coil and a switching means in parallel with the capacitor, the number of these series circuits being equal to the number of engine cylinders.

In the known ignition systems, semiconductor switching elements such as thyristors or transistors are customarily used as the switching means. In response to the conduction of the switching element in one of the series circuits, the charge stored in the capacitor is discharged by way of the series circuit and a high voltage is induced in a secondary winding of the ignition coil in the specific series circuit so that an ignition spark jumps across the spark gap of the associated ignition plug. However, the known ignition system of this kind has been defective in that the voltage induced due to the discharge of the capacitor may be applied to the switching element in another series circuit thereby turning on such switching element with the result that all the charge stored in the capacitor cannot be supplied to the former series circuit. Further, due to the fact that the discharge current is also supplied to the ignition coil in the latter series circuit, a high voltage is prematurely induced in the secondary winding of the latter ignition coil before the ignition period is reached, resulting in mal-operation or preignition. Thus, difficulty in attaining proper ignition control has been frequently encountered with the known ignition system of this kind.

SUMMARY OF THE INVENTION

It is a primary object of the present invention to provide a novel and useful ignition system which is free from the above defects and can reliably operate with an improved and stable ignition performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an electrical circuit diagram of an embodiment of the ignition system according to the present invention.

FIG. 2 is an electrical circuit diagram showing in detail the structure of a d.c. -- a.c. converter shown in FIG 1.

FIGS. 3a, 3b, 3c and 3d show voltage waveforms for illustrating the operation of the ignition system shown in FIG. 1.

FIG. 4 is an electrical circuit diagram showing the structure of another form of switching means shown in FIG. 1.

FIG. 5 is an electrical circuit diagram of another embodiment of the present invention.

FIG. 6 is a sectional view showing the structure of a magneto generator and ignition signal supplying means shown in FIG. 5.

FIG. 7 is a section taken on the line VII-VII' in FIG. 6.

FIGS. 8a, 8b, 8c, 8d and 8e show voltage waveforms for illustrating the operation of the ignition system shown in FIG. 5.

FIG. 9 is an electrical circuit diagram of a further embodiment of the present invention.

FIG. 10 is a sectional view showing the structure of a magneto generator and ignition signal supplying means shown in FIG. 9.

FIG. 11 is a section taken on the line XI-XI' in FIG. 10.

FIG. 12 is an electrical circuit diagram of another embodiment of the present invention.

FIG. 13 is a sectional view showing the structure of one form of a magneto generator and ignition signal supplying means shown in FIG. 12.

FIG. 14 is a sectional view showing the structure of another form of the magneto generator and ignition signal supply means shown in FIG. 12.

FIGS. 15a, 15b, 15c, 15d and 15e and FIGS. 16a, 16b, 16c, 16d and 16e show voltage waveforms for illustrating the operation of the ignition system shown in FIG. 12.

FIG. 17 is an electrical circuit diagram showing another form of electrical connection for an ignition coil in the first, second, third and fourth embodiments of the present invention.

FIG. 18 is an electrical circuit diagram showing another form of electrical connecton between an igniton coil and an ignition plug in the embodiments of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 showing a first embodiment of the present invention, the positive terminal of a battery 1, whose negative terminal is grounded, is connected to a d.c. -- a.c. converter 3 through an ignition switch 2. The d.c. -- a.c. converter 3 is of the blocking oscillator type which converts a low d.c. output voltage of the battery 1 into a high a.c. voltage and is composed of a bias resistor 3a, a transistor 3b, a feedback resistor 3c, a feedback capacitor 3d, a transformer 3e and a voltage spike removing capacitor 3f as show n FIG. 2. The a.c. voltage produced by the d.c. - a.c. converter 3 is subject to half-wave rectification by a diode rectifier 4 which is connected to the opposite terminals A and B of a capacitor 6 by way of respective resistors 5a and 5b. One of the terminals A of the capacitor 6 is connected to chassis ground across a primary winding 7a.sub.1 of an ignition coil 7a and across the anode and cathode of a controlled rectifier or thyristor 8a, while the other terminal B is connectd to chassis ground across a primary winding 7 b.sub.1 of another ignition coil 7b and across the anode and cathode of another controlled rectifier or thyristor 8b. The former terminal A of the capacitor 6 is further conected to chassis ground through a diode 9a which constitutes a discharging circuit together with the primary winding 7a.sub.1 of the ignition coil 7aand the thyristor 8a, while the latter terminal B is similarly conneted to chassis ground through another diode 9b which constitutes a discharging circuit together with the primary winding 7b.sub.1 of the ignition coil 7b and the thyristor 8b. These diodes 9a and 9 b are conected at their anode to the chassis ground as shown in FIG. 1. The respective gates of the thyristors 8a and 8b are connected to breakers 10a and 10b, and the common junction points C and D between these elements are connected to the positive terminal of the battery 1 through respective resistors 11a and 11b and ignition switch 2. The breakers 10a and 10b are alternately turned on and off in synchronism with the rotation of the engine. Secondary windings 7a.sub.2 and 7b.sub.2 of the ignition coils 7a and 7b are connectd to ignition plugs 12a and 12b, and diodes 13a and 13b are connected across the primary windings 7 a.sub.1 and 7b.sub.1 of the ignition coils 7a and 7b for absorbing backward voltage, respectively.

In operation, the ignition switch 2 is turned on when starting the engine, and an ignition signal appears in response to the operation of the breakers 10a and 10b. The waveform of the ignition signal appearing at the point C in response to the operation of the breaker 10 a is shown in FIG. 3 c, and the waveform of the ignition signal appearing at the point D in response to the operation of the breaker 10b is shown in FIG. 3d.

When the breaker 10a is turned off at time t.sub.1 in FIG. 3c, the ignition signal is applied to the gate of the thyristor 8a, and the terminal A of the capacitor 6 is shorted to chassis ground due to the conduction of the thyristor 8a, thereby completing a charging circuit which is traced from the power source 1 -- d.c. - a.c. converter 3 -- diode 4 -- resistor 5b -- terminal B of capacitor 6 -- terminal A of capacitor 6 -- primary winding 7a.sub.1 of ignition coil 7a -- thyristor 8a to chassis ground. As a result, the capacitor 6 is charged in the state in which the terminal B is positive relative to the terminal A. The manner of charging is shown in FIG. 3b in which it will be seen that the capacitor 6 is charged stepwise over several cycles of the a.c. voltage. The charging operation continues until the ignition signal disappears due to the turning on of the breaker 10a at time t.sub.2 or until the no-load a.c. voltage level is reached, and at this time t.sub.2, the charging opeation is completed.

The breaker 10b is tuned off at time t.sub.3 in FIG. 3d and the ignition signal appears at the point D. The thyristor 8b conducts and the charge stored in the capacitor 6 is discharged through a discharging circuit which is traced from the terminal B of capacitor 6 -- primary winding 7b.sub.1 of ignition coil 7b -- thyrisotr 8b -- chassis ground-- diode 9b to the other terminal A of the capacitor 6. A high ignition voltage is induced in th secondary winding 7 b.sub.2 of the ignition coil 7b and an ignition spark jumps across the spark gap of the ignition plug 12b. At the same time, the next charging operation for the capacitor 6 is started. More precisely, a charging cicuit which is traced from the power source 1-- d.c. - a.c. converter 3 -- diode 4 -- resistor 5a -- terminal A of capacitor 6 terminal B of capacitor 6 -- primary windng 7b.sub.1 of ignition coil 7b -- thyristor 8b to chassis ground is completed due to the conduction of the thyristor 8 b, and the charging operation for the capacitor 6 is started in a direction opposite to that above described, that is, in the state in which the terminal A is now positive relative to the terminal B. The capacitor 6 is charged stepwise as shown in FIg. 3a, and the charging operation continues until the ignition signal disappears due to the turning on of the breaker 10b at time t.sub.4 or until the no-load a.c. voltage level is reached. The charging operation is completed at this time t.sub.4. The ignition signal appears again at time t.sub.5 FIG. 3c and the thyristor 8a conducts again, thereby completing a discharging circuit which is traced from the terminal A of the capacitor 6 -- primary winding 7a.sub.1 of ignition coil 7 a -- thyristor 8a -- chassis ground -- diode 9a to the terminal B of the capacitor 6. Discharge current flows through the primary winding 7a.sub.1 of the ignition coil pg,8 7aand a high ignition voltage is induced in the secondary winding 7a.sub. 2 of the ignition coil 7a so that an ignition spark jumps across the spark gap of the ignition plug 12a.

It will be understood from the above description that, in the first embodiment of the present invention, the single capacitor 6 is charged alternately in opposite directions in response to the two ignition signals and the capacitor discharge current is alternately distributed to the two ignition coils 7a and 7b. Thus, mal-operation of the semiconductor switching elements or thyristors 8a and 8b, which may result from external noise including ignition sparks, would not in any way adversely affect the ignition performance of the ignition system which can therefore operate stably.

The semiconductor switching elements 8a and 8b shown in FIG. 1 may be replaced by transistors 14a and 14b as shown in FIG. 4.

In a second embodiment of the present invention shown in FIG. 5 in which like reference numerals are used to denote like parts appearing in FIG. 1, a magneto generator 16 incorporating a pair of capacitor charging coils 15a and 15b therein is provided to serve as a power source for charging a capacitor 6. Means for applying an ignition signal to controlled rectifiers or thyristors 8a and 8b includes a pair of ignition signal generators 18 a and 18b having ignition signal generating coils 17a and 17 b respectively. The capacitor charging coils 15a and 15b are grounded at one end thereof and are connected at the other end thereof to the opposite terminals A and B of the capacitor 6 through diode rectifiers 4 a and 4 b respectively. The ignition signal generating coils 17a and 17b are grounded at one end thereof and are connected at the other end thereof to the gates of the thyristors 8a and 8b through diode rectifiers 19and 19b respectively. The mechanical structure of the magneto generator 16 and ignition signal generators 18a and 18b will be described with reference to FIGS. 6 and 7.

The magneto generator 16 includes a rotor 16a which is driven by the crankshaft 20 of an internal combustion engine. The rotor 16a comprises a generally cup-shaped body 23 of iron, four radially magnetized magnets 22a, 22b, 22c and 22d, and four pole pieces 21a, 2b, 21c and 21d. These magnets and pole pieces are disposed on the inner periphery of the cup-shaped body 23 in an equally circumferentially spaced relationship so that the adjacent pole pieces have polarities opposite to each other as shown. A lug 23a of magnetic material is provided at a suitable position on the outer periphery of the cup-shaped body 23.

Two stators 16b and 16c are fixedly mounted on a stationary base plate 24 opposite to the pole pieces 21a, 21b, 21c and 21d of the rotor 16a. The latter stator 16c comprises an iron core 25b and a coil 25a mounted on the iron core 25b and is provided for supplying electric power to electric loads except the ignition means, such as lamps and battery charging means not shown in FIG. 5. The former stator 16b comprises a pair of iron core portions 15a' and 15b' which are radially juxtaposed and magnetically coupled to each other, and the capacitor charging coils 15a and 15b are mounted on these iron core portions 15a' and 15b' respectively. The pole pieces 21a, 21b, 21c and 21d of the rotor 16a are common to these coils 15a and 15b too.

The ignition signal generating coils 17a and 17b are mounted on timing cores 26a and 26b respectively. These timing cores 26a and 26b are bonded at one or outer end thereof to one end of magnets 27a and 27b which are bonded at the other end thereof to one of the arms of generally L-shaped cores 28a and 28b respectively. The elements 17a, 26a, 27a and 28a are enclosed in a mass of non-magnetic material 29a to constitute a unit 30a, while the elements 17b, 26b, 27b and 28b are similarly enclosed in a mass of non-magnetic material 29b to constitute another unit 30b. These units 30a and 30b are suitably secured to a stationary part (not shown) in the vicinity of the magneto generator 16 in such a manner that the inner end of each of the timing cores 26a and 26b is cyclically brought to a position opposite to the lug 23a on the rotor 16a during rotation of the rotor 16a and the inner end of the other arm of each of the L-shaped cores 28a and 28b is opposite to the outer peripheral surface of the rotor 16a. As the lug 23a on the rotor 16a moves relative to the timing cores 26a and 26b, a change in the magnetic reluctance occurs in the magnetic circuits including respectively the magnets 27a and 27b, timing cores 26a and 26b, lug 23a on the rotor 16a, cup-shaped body 23 and cores 28a and 28b, and due to the variations in the magnetic flux, two ignition signals 180.degree. out of phase from each other are alternatively generated by the respective ignition signal generating coils 17a and 17b.

The operation of the second embodiment of the present invention will be described with reference to FIG. 5 and FIGS. 8a to 8e. FIG. 8a shows the waveform of no-load voltage appearing across the capacitor charging coils 15a and 15b. FIG. 8b shows the voltage waveform of the ignition signal applied to the gate of the thyristor 8a from the ignition signal generating coil 17a. FIG. 8c shows the voltage waveform of the ignition signal applied to the gate of the thyristor 8b from the ignition signal generating coil 17b. In FIGS. 8a to 8e, the waveforms are plotted on the same time axis, with the horizontal axis representing time t and the vertical axis representing voltage v. Suppose that the voltage waveforms have a predetermined phase relationship as seen in FIGS. 8a, 8b and 8c. At time t.sub.1 in FIG. 8, the voltage generated across the capacitor charging coil 15a starts to increase toward the positive side and the ignition signal having the waveform shown in FIG. 8b is applied to the gate of the thyristor 8a so that the thyristor 8a conducts. Due to the condution of the thyristor 8a, the charge stored in the capacitor 6 is discharged through a primary winding 7a.sub.1 of an ignition coil 7a, thyristor 8a and diode 9a with the result that a high voltage is induced in a secondary winding 7a.sub.2 of the ignition coil 7a and an ignition spark jumps across the spark gap of an ignition plug 12a. At the same time the capacitor charging coil 15a is shorted to chassis ground through the primary winding 7a.sub.1 of the ignition coil 7a and the thyristor 8a. Due to the flow of short-circuit current through the capacitor charging coil 15a, magnetic flux corresponding to the inverse ampere-turns is produced in the iron core porton 15a' mounting the capacitor charging coil 15a thereon, and as a result, almost all the magnetic flux emanating from the pole pieces passes through the other iron core bportion 15b' where the magnetic reluctance is less than that of the iron core portion 15a' of the stator 16b, thereby inducing a voltage in the capacitor charging coil 15b mounted on the iron core portion 15b'. This induced voltage charges the capacitor 6 through a circuit which is traced from the coil 15b -- diode 4b -- capacitor 6 -- primary winding 7a.sub.1 of ignition coil 7a -- thyristor 8a to chassis ground. FIG. 8d shows the manner of potential build-up at the terminal B during the charging of the capacitor 6. After the capacitor 6 has been charged, the polarity of the voltage generated across the capacitor charging coil 15a is reversed and the thyristor 8a is reversed biased to be cut off. At time t.sub.2 in FIG. 8, the voltage generated across the capacitor charging coil 15b starts to increase toward the positive side and the ignition signal having the waveform shown in FIG. 8c is applied to the gate of the thyristor 8b so that the thyristor 8b conducts. Due to the conduction fo the thyristor 8b, the charge stored in the capacitor 6 is discharged through a discharging circuit which is traced from one terminal B of capacitor 6 -- primary winding 7b.sub.1 of ignition coil 7b -- thyristor 8b -- chassis ground -- diode 9b to the other terminal A of capacitor 6, with the result that a high voltage is induced in a secondary winding 7b.sub.2 of the ignition coil 7b and an ignition sparks jumps across the spark gap of an ignition plug 12b. At the same time, the capacitor charging coil 15b is shorted to chassis ground through the primary winding 7b.sub.1 of the ignition coil 7b and the thyristor 8b, and a voltage is induced in the capacitor charging coil 15a in the manner described previously. This induced voltage harges the capacitor 6 through a circuit which is traced from the coil 15a -- diode 4a -- capacitor 6 -- primary winding 7b.sub.1 of ignition coil 7b --thyristor 8b to chassis ground. FIG. 8 shows the manner of potential build-up at the terminal A during the charging of the capacitor 6. Thereafter, the above operation is repeated to cause alternate jumping of ignition sparks across the spark gap of the ignition plugs 12a and 12b.

It is to be noted that the current which flows from the capacitor charging coils 15a and 15b into the primary windings 7a.sub.1 and 7a.sub.2 of the ignition coils 7a and 7b is of the order of one one-hundredth of the discharge current of the capacitor 6. Thus, there is utterly no fear that any direct ignition is caused by the current flowing out of the capacitor charging coils 15a and 15b.

In a third embodiment of the present invention shown in FIG. 9 in which like reference numerals are used to denote like parts appearing in FIG. 5, a magneto generator 16 incorporating a single capacitor charging coil 15 therein cooperates with a transformer 31 to serve as a power source for charging a capacitor 6. The magneto generator 16 has a structure as shown in FIGS. 10 and 11 and differs from the magneto generator shown in FIG. 6 and 7 in that one of the stators 16b and 16c, or more specifically, the stator 16b comprises a single iron core 15' mounting the capacitor charging coil 15 thereon. the transformer 31 comprises a primary coil 31a, two secondary coils 31b and 31c, and thre cores 31d, 31e and 31f mounting these coils 31a, 31b and 31c independently of one another. The first core 31d mounting the primary coil 31a thereon and the second core 31e mounting the first secondary coil 31b thereon constitute a first closed magnetic circuit, while the first core 31d mounting the primary coil 31a thereon and the third core 31f mounting the second secondary coil 31c thereon constitute a second closed magnetic circuit. The primary and secondary coils 31a, 31b and 31c are grounded at one end thereof, and the primary coil 31a is connected at the other end thereof to the capacitor charging coil 15, while the secondary coils 31b and 31c are connected at the other end thereof to respective diode rectifiers 4a and 4b. In this embodiment, the energy produced by the capacitor charging coil 15 is transferred to the primary coil 31a of the transformer 31 act in the entirely same manner as the capacitor charging coils 15a and 15b in the second embodiment.

In the third embodiment of the present invention, the capacitor charging coil 15 is not intended for directly charging the capacitor 6 but is provided for the purpose of transferring the magnetic energy produced by the magneto generator 16 to the transformer 31. Therefore, a high output voltage is not required and fine wire need not be coiled. Fine wire is only required for the coils mounted on the cores of the transformer 31 and this can be easily done by a technically established process. Thus, the ignition system can operate with a stable ignition performance.

In a fourth embodiment of the present invention shown in FIG. 12 in which like reference numerals are used to denote like parts appearing in FIG. 9, a magneto generator 16 incorporating a single capacitor charging coil 15 therein is provided to serve as a power source for charging a capacitor 6, and the opposite ends of the capacitor charging coil 15 are connected to respective diode rectifiers 4a and 4b. A pair of diodes 9a and 9b forming part of discharging circuit for the capacitor 6 are connected beteen chassis ground and the common junction points E and F between the coil 15 and the rectifier diodes 4a and 4b, so that these four diodes constitute a full-wave rectifier circuit for the full-wave rectification of the voltage appearing across the coil 15.

FIG. 13 shows the structure of the magneto generator 16 when it is of the six-pole type. The magneto generator 16 of the six-pole type comprises a rotor 16a and three stators 16b, 16c.sub.1 and 16c.sub.2. The rotor 16a includes six pole pieces 21a, 21b, 21c, 21d, 21e and 21f and six magnets 22a, 22b, 22c, 22d, 22e and 22f. The stator 16b includes an iron core 15' mounting the capacitor charging coil 15 thereon, while the other two stators 16c.sub.1 and 16c.sub.2 are similar in function to the stator 16c shown in FIG. 10.

The operation of the ignition system shown in FIG. 12 will be described with reference to the case in which the six-pole magneto generator 16 shown in FIG. 13 is used. FIG. 15a shows the waveform of no-load voltage generating across the capacitor charging coil 15 and appearing at the point F when the other point E is taken as a reference point. FIG. 15b shows the voltage waveform of the ignition signal applied to the gate of a thyristor 8a from an ignition signal generating coil 17a, FIG. 15c shows the voltage waveform of the ignition signal applied to the gate of a thyristor 8b from an ignition signal generating coil 17b. In FIGS. 15a to 15e, the waveforms are plotted on the same time axis, with the horizontal axis representing time t and the vertical axis representing voltage v. Suppose that the voltage waveforms have a predetermined phase relationship as seen in FIGS. 15a, 15b and 15c. At time t.sub.1 in FIG. 15, the voltage appearing at the point F starts to increase toward the positive side, and the ignition signal having the waveform shown in FIG. 15b is applied to the gate of the thyristor 8a from the ignition signal generating coil 17a so that the thyristor 8a conducts. Due to the conduction of the thyristor 8a, the capacitor 6 is charged through a circuit which is traced from one terminal of the capacitor charging coil 15 -- diode 4b -- capacitor 6 -- primary winding 7a.sub.1 of ignition coil 7a -- thyristor 8a -- chassis ground -- diode 9a to the other terminal of the capacitor charging coil 15. FIG. 15d shows the manner of potential build-up at the terminal B of the capacitor 6 during the charging of the capacitor 6. After the capacitor 6 has been charged, the polarity of the voltage generating across the capacitor coil 15 is reversed, and the thyristor 8a is reverse biased to be cut off. At time t.sub.2 in FIG. 15, the voltage appearing at the point E starts to increase toward the positive side and the ignition signal having the waveform shown in FIG. 15c is applied to the gate of the thyristor 8b from the ignition signal generating coil 17b so that the thyristor 8b conducts. Due to the conduction of the thyristor 8b, the charge stored in the capacitor 6 is discharged through a discharging circuit which is traced from one terminal B of capacitor 6 -- primary winding 7b.sub.1 of ignition coil 7b -- thyristor 8b -- chassis ground -- diode 9b -- diode 4a to the other terminal A of the capacitor 6, with the result that a high voltage is induced in a secondary winding 7b.sub.2 of the ignition coil 7b and an ignition spark jumps across the spark gap of an ignition plug 12b. At the same time, the voltage generated across the capacitor charging coil 15 charges the capacitor 6 through a circuit which is traced from the coil 15 -- diode 4a -- capacitor 6 -- primay winding 7a.sub.1 of ignition coil 7a -- thyristor 8b -- chassis ground to the diode 9b, and the capacitor 6 is now charged in such a manner that the terminal A is positive relative to the terminal B in FIG. 12. FIG. 15e shows the manner of potential build-up at the terminal A during the charging of the capacitor 6.

Thereafter, the above operation is repeated to cause alternate jumping of ignition sparks across the spark gap of the ignition plugs 12a and 12 b.

It will be understood from the above description that the fourth embodiment of the present invention takes full advantage of the fact that the polarity of the voltage generated across the capacitor charging coil 15 in the six-pole magneto generator 16 is reversed every 180.degree.. The output terminals of the capacitor charging coil 15 are connected through the full-wave rectifier circuit to the capacitor 6 for charging the capacitor 6, and the ignition signals which are 180.degree. out of phase from each other are applied alternately to the two thyristors 8a and 8b. Thus, this embodiment is advantageous in that the capacitor 6 can be charged in opposite directions by the voltage generated across the single capacitor charging coil 15 and that the ignition system has a very simple and compact construction.

FIG. 14 shows the structure of anotheform of the magneto generator 16 shown in FIG. 12. More precisely, it shows the structure of a four-pole magneto generator preferably use in the ignition system shown in FIG. 12. Referring to FIG. 14, the magneto generator 16 has the entirely same internal structure as that shown in FIG. 10 except that it differs merely from the latter in that an additional lug 23b of magnetic material is provided on the outer periphery of the generally cup-shaped body 23 at a position spaced apart by 90.degree. from the lug 23a of magnetic material. The inner end of each timing cores 26a and 26b is cyclically brought to a position opposite to the lugs 23a and 23b on the rotor 16a. As the lugs 23a and 23b on the rotor 16a move relative to the timing cores 26a and 26b, a change in the magnetic reluctance occurs in the magnetic circuits including respectively magneto 27a and 27b, timing cores 26a and 26b, lugs 23a and 23b on the rotor 16a, cup-shaped body 23 and cores 28a and 28b, and due to the variations in the magnetic flux, a set of ignition signals 90.degree. out of phase from each other are generated by each of the ignition signal generating coils 17a and 17b so that, during one rotation of the rotor 16a, these two sets of ignition signals occur alternately in a 180.degree. spaced apart relationship from each other.

The operation of the ignition system shown in FIG. 12 will be described with reference to the case in which the four-pole magneto generator 16 shown in FIG. 14 is used. FIG. 16a shows the waveform of no-load voltage generated across the capacitor charging coil 15 and appearing at the point F when the other point E is taken as a reference point. FIG. 16b shows the voltage waveform of the ignition signal applied to the gate of the thyristor 8a from the ignition signal generating coil 17a. FIG. 16c shows the voltage waveform of the ignition signal applied to the gate of the thyristor 8b from the ignition signal generating coil 17b. In FIGS. 16a to 16e, the waveforms are plotted on the same time axis, with the horizontal axis representing time t and the vertical axis representing voltage v. Suppose that the voltage waveforms have a predetermined relationship as seen in FIGS. 16a, 16b and 16c. At time t.sub.1 in FIG. 16, the voltage appearing at the point F starts to increase toward the positive side and the ignition signal having the waveform shown in FIG. 16b is applied to the gate of the thyristor 8a from the ignition signal generating coil 17a so that the thyristor 8a conducts. Due to the conduction of the thyristor 8a, the charge stored in the capacitor 6 is discharged through the primary winding 7a.sub.1 of the ignition coil 7a and the thyristor 8a with the result that an ignition spark jumps across the spark gap of the ignition plug 12a. At the same time, the voltage generated across the capacitor charging coil 15 charges the capacitor 6 through a circuit which is traced from one terminal of the capacitor coil 15 -- diode 4b -- capacitor 6 -- primary winding 7a.sub.1 of ignition coil 7a -- thyristor 8a -- chassis ground -- diode 9b to the other terminal of the capacitor charging coil 15. FIG. 16d shows the manner of potential build-up at the terminal B in FIG. 12 during the charging of the capacitor 6. After the capacitor 6 has been charged, the polarity of the voltage generated across the capacitor charging coil 15 is reversed, and the thyristor 8a is reversed biased to be cut off. At time t.sub.2 in FIG. 16, the voltage appearing at the point E starts to increase toward the positive side and the ignition signal having the waveform shown in FIG. 16b is applied to the thyristor 8a from the ignition signal generating coil 17a, thereby completing a circuit which is traced from one terminal of the capacitor charging coil 15 -- diode 4a -- primary winding 7a.sub.1 of ignition coil 7a -- thyristor 8a -- chassis ground -- diode 9a to the other terminal of the capacitor charging coil 15. Although this circuit does not contribute to the charging of the capacitor 6, it prevents the capacitor charging coil 15 from operating with no load and protects the circuit elements against undesirable breakdown. At time t.sub.3 in FIG. 16, the voltage appearing at the point F starts to increase toward the positive side again and the ignition signal having the waveform shown in FIg. 16c is applied to the gate of the thyristor 8b from the ignition signal generating coil 17b so that the thyristor 8b conducts. Due to the conduction of the thyristor 8b, the charge stored in the capacitor 6 is discharged through a discharging circuit which is traced from one terminal B of the capacitor 6 -- primary winding 7b.sub.1 of ignition coil 7b -- thyristor 8b -- chassis ground -- diode 9b -- diode 4a to the other terminal A of the capacitor 6, with the result that a high voltage is induced in the secondary winding 7b.sub.2 of the ignition coil 7b and an ignition spark jumps across the spark gap of the ignition plug 12b. At the same time, the capacitor charging coil 15 is shorted to chassis ground through a circdui which is traced from one terminal of the capacitor charging coil 15 -- diode 4b -- primary winding 7b.sub.1 of ignition coil 7b -- thyristor 8b -- chassis ground -- diode 9b to the other terminal of the coil 15. Although this circuit does not contribute to the charging of the capacitor 6 like the previously described circuit, it prevents the capacitor charging coil 15 from operating with no load and protects the circuit elements against undesirable breakdown.

At time t.sub.4 shown in FIG. 16, the voltage appearing at the point E starts to increase toward the positive side and the ignition signal shown in FIG. 16c is applied to the gate of the thyristor 8b with the ignition signal generating coil 17b so that the thyristor 8b conducts. Due to the conduction of the thyristor 8b, the voltage generated across the capacitor charging coil 15 charges the capacitor 6 through a circdit which is traced from one terminal of the capacitor charging coil 15 -- diode 4a -- capacitor 6 -- primary winding 7b.sub.1 of ignition coil 7b -- thyristor 8b -- chassis ground -- diode 9a to the other terminal of the coil 15, and the capacitor 6 is now charged in such a manner that the terminal A is positive relative to the terminal B in FIG. 12. FIG. 16e shows the manner of potential build-up at the terminal A during the charging of the capacitor 6. Thereafter, the above operation is repeated to cause alternate jumping of ignition sparks across the spark gap of the ignition plugs 12a and 12b.

It will be understood from the above description that, in the ignition system including the four-pole magneto generator, the output terminals of the capacitor charging coil 15 are connected through the full-wave rectifier means to the capacitor 6 for charging the capacitor 6 and a set of ignition signals 90.degree. out of phase from each other are are alternately to each of the thyristors 8a and 8b in such a relationship that these two sets of ignition signals are 180.degree. spaced apart from each other. This arrangement is advantageous in that the capacitor 6 can be charged in opposite directions by the the voltage generated across the single capacitor charging coil 15. Thus, not only the ignition system has a very simple and compact construction, but also the capacitor charging coil 15 is prevented from operating with no load and the circuit elements can be protected against undesirable breakdown. In the embodiments of the present invention above described, the ignition coils 7a and 7b may be arranged so that their primary windings 7a.sub.1 and 7b.sub.1 are connected in series with the respective diodes 9a and 9b between the capacitor 6 and chassis ground as shown in FIG. 17. Further, an ignition system for a four-cycle four-cylinder engine can be easily realized by connecting ignition plugs 12a.sub.1, 12a.sub.2, 12b.sub.1 and 12b.sub.2 across the secondary windings 7a.sub.2 and 7b.sub.2 of the ignition coils 7a and 7b respectively as shown in FIG. 18.

Claims

I claim:

1. An ignition system for use in a multicylinder internal combustion engine each cylinder of which has at least one spark plug comprising a capacitor, a power source for charging said capacitor, a first charging circuit including a series connection of said power source, said capacitor and a first switching means controlling the charge-discharge of said capacitor so that current supplied from said power source can pass successively through said capacitor and said first switching means, a second charging circuit including a series connection of said power source, said capacitor and a second switching means controlling the charge-discharge of said capacitor so that current supplied from said power source can pass successively through said capacitor and said second switching means, a first discharging circuit including a series connection of said capacitor, said first switching means and a first diode so that the discharge stored in said capacitor can be discharged through said first switching means and said first diode, a second discharging circuit including a series connection of said capacitor, said second switching means and a second diode so that the charge stored in said capacitor can be discharged through said second switching means and said second diode, and a first and a second ignition coils each including a primary and a secondary windings, said first and second charging circuits being arranged to charge said capacitor in directions opposite to each other, said primary windings of said first and second ignition coils being connected in series with said first and second switching means in such circuit portions of said first and second discharging circuits where said two discharging circuits do not overlap each other, and each of said secondary windings of said first and second ignition coils being connectable to each of said spark plug.

2. An ignition system as claimed in claim 1, in which said capacitor charging power source comprises a magneto generator having a pair of capacitor charging coils therein, one of said capacitor charging coils being disposed in said first charging circuit, while the other said capacitor charging coil being disposed in said second charging circuit, and a pair of current rectifying diodes are connected between said capacitor charging coils and said capacitor in series therewith in said first and second charging circuits respectively.

3. An ignition system as claimed in claim 1, in which said capacitor charging power source comprises a magneto generator having a single capacitor charging coil therein, a transformer operatively connected to said magneto generator, said transformer including a first, a second and a third cores, a primary coil wound on said first core and connected to said capacitor charging coil, a first and a second secondary coils wound on said second and third cores and connected to said first and second charging circuits respectively, whereby a first closed magnetic circuit is formed by said first core mounting said primary coil thereon and said second core mounting said first secondary coil thereon, and a second closed magnetic circuit is formed by said first core and said third core mounting said second secondary coil thereon, and a pair of current rectifying diodes are connected between said first and second secondary coils of said transformer and said capacitor in series therewith in said first and second charging circuits respectively.

4. An ignition system as claimed in claim 1, in which said capacitor charging power source comprises a magneto generator having a single capacitor charging coil therein, both ends of said capacitor charging coil being connected to said first and second charging circuits respectively, and a pair of current rectifying diodes are connected between said capacitor charging coil and said capacitor in series therewith in such circuit portions of said first and second charging circuits where said charging circuits overlap said first and second discharging circuits respectively.

5. An ignition system as claimed in claim 4, in which said magneto generator is provided with six poles.

6. An ignition system as claimed in claim 4, in which said magneto generator is provided with four poles, and said first and second switching means comprises a first and a second thyristors having a gate respectively and a first and a second ignition signal supplying means connected to the gate of said first and second thyristors respectively, said first and second ignition signal supplying means being adapted to apply alternately a set of two ignition signals to the gate of said first and second thyristors respectively in a 180.degree. spaced apart relationship, the ignition signals in each set being 90.degree. out of phase from each other in the angular position of rotation of said magneto generator.