Ignition system for internal combustion engines

An ignition system for internal combustion engines comprising an ignition coil (38), a power circuit (30) including a converter for converting the output of a battery (31) into a high voltage, a capacitor (37) arranged at the primary side of the ignition coil (38) and charged by the output from the power circuit (30), a discharging control thyristor (41) which conducts at a spark-timing of an internal combustion engine to discharge electric charges in the capacit of (37) into the primary winding (38a) of the ignition coil (38) and converter control means (49, 52) which makes the converter inactive earlier than the input of a trigger signal to the gate of the thyristor (41) by a first predetermined time (t.sub.1), and which makes the converter active again in a second predetermined time (t.sub.2) since the thyristor (41) has been triggered to conduct.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an ignition system for internal combustion 
engines, and is more particularly concerned with an ignition system for 
internal combustion engines which ensures ignition. 
2. Discussion of Background 
Referring to FIG. 3, there is shown a schematic circuit diagram of a 
conventional ignition system for internal combustion engines, which has 
been disclosed in e.g. Japanese Unexamined Patent Publication No. 
148071/1989. In FIG. 3, reference numeral 1 designates a power circuit. 
The power circuit is constituted by a battery 2 and a converter. The 
converter includes a transformer 3 connected to the battery 2, a 
transistor 4 connected to a transformer 3, a transistor 5 connected to the 
base of the transistor 4, a diode 7 connected to the base of the 
transistor 5, and an oscillation circuit 8 connected to the diode 7. The 
transformer 3 has the secondary winding connected to the primary winding 
of an ignition coil 11 through a diode 9 and a capacitor 10. The ignition 
coil 11 has the secondary winding connected to a spark plug 12. The 
capacitor 10 has one end grounded through a diode 13. The capacitor 10 has 
the other end grounded through a discharge control thyristor 14. The 
thyristor 14 has the gate connected to a signal coil 16 through a 
spark-timing control circuit 15. Reference numeral 17 designates a power 
supply prevention circuit which includes a comparator 18. The comparator 
has a noninverted terminal connected to the gate of the thyristor 14. The 
comparator has an inverted terminal connected to the junction between 
reference resistors 19 and 20. The comparator has an output terminal 
connected to the base of the transistor 5 through a diode 22. Reference 
number 21 designates a resistor which is connected to the output terminal 
of the comparator 18. 
The operation of the conventional ignition system shown in FIG. 3 will be 
described. The voltage from the battery 2 is increased to a high level by 
the transformer 3. The high voltage is rectified by the diode 9, and 
charges a capacitor 10. A signal which is generated from the signal coil 
16 in synchronism with engine speed is supplied to the gate of the 
thyristor 14 through the spark-timing control circuit 15, thereby causing 
the thyristor 14 to conduct. As a result, the electric charges stored in 
the capacitor 10 are discharged through the thyristor 14 and the primary 
winding of the ignition coil 11 to cause a high voltage to generate at the 
secondary winding of the ignition coil 11, thereby firing the spark plug 
12. 
The voltage across the gate and the cathode of the thyristor 14 which is 
indicated by V.sub.g at FIG. 4(a) is supplied to the comparator 18 to be 
compared to a set voltage V.sub.r. When the voltage V.sub.g across the 
gate and the cathode achieves the set voltage V.sub.r or more, an output 
shown in FIG. 4(b) is obtained at the output of the comparator 18 to turn 
on the transistor 5. As a result, the transistor 4 is turned off to obtain 
the collector voltage in the form shown in FIG. 4(c), thereby 
substantially forcing oscillation to stop. In this manner, the output from 
the power circuit 1 is prevented from being supplied to the capacitor 10. 
As stated earlier, the conventional ignition system detects the voltage 
across the gate and the cathode of the thyristor 14 before stopping 
oscillation. This arrangement creates a problem in that the magnetic 
energy which has been stored in the transformer 3 is discharged to the 
thyristor 14 just before oscillation stoppage, and the thyristor 14 is 
kept conducting for a long period to shorten the subsequent oscillation 
charging period, causing the capacitor 10 to be charged in an incomplete 
manner. 
The effect which is given by the continuous conduction of the thyristor 14 
for such long period grows great in particular at high engine speed 
because the cycle from one spark from the following spark is shortened. 
This creates another problem in that the thyristor 14 could be ultimately 
kept conducting until the following spark-timing, causing misfire. 
In addition, because oscillation starts immediately when the voltage across 
the gate and the cathode of the thyristor 14 lowers, a voltage could be 
applied to the thyristor 14 by the power circuit 1 before the withstand 
voltage of the thyristor 14 has fully revived. This means that there is a 
possibility that the thyristor 14 is conducted again to short-circuit the 
output of the power circuit 1, creating another problem in that the 
capacitor 10 is charged in an incomplete manner. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to dissolve these problems and to 
provide an ignition system for internal combustion engines, capable of 
obtaining a high capacitor charging voltage in a stable manner even if the 
engine is rotated at high speed. 
The foregoing and other objects of the present invention have been attained 
by an ignition system for internal combustion engines comprising an 
ignition coil; a power circuit including a converter for converting the 
output of a battery into a high voltage; a capacitor arranged at the 
primary side of the ignition coil and charged by the output from the power 
circuit; a discharging control thyristor which conducts at a spark-timing 
of an internal combustion engine to discharge electric charges in the 
capacitor into the primary winding of the ignition coil, and converter 
control means which makes the converter inactive earlier than the input of 
a trigger signal to the gate of the thyristor by a first predetermined 
time, and which makes the converter active again in a second predetermined 
time since the thyristor has been triggered to conduct. 
In accordance with the present invention, oscillation ceases earlier than 
the triggering of the discharge control thyristor by the first 
predetermined time. The oscillation restarts in the second predetermined 
time since the thyristor has been triggered to conduct. 
The present invention can provide the ignition system which is capable of 
obtaining a stable and high capacitor charging voltage to ensure a spark 
for operating an engine even if the engine is rotating at a high speed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, and more particularly to FIG. 1 thereof, 
there is shown a schematic circuit diagram showing an embodiment of the 
ignition system according to the present invention. In FIG. 1, reference 
numeral 30 designates a power circuit which includes a converter, which 
will be explained below. The power circuit is constituted by a battery 31 
and the converter. The converter comprises a transformer 32, an 
oscillation transistor 33, a capacitor 34, resistors 35 and 35a, and a 
rectifier diode 36. The battery 31 is grounded through the primary winding 
32a of the transformer 32 and the collector to emitter connection of the 
transistor 33, and is also connected to the base of the transistor 33 
through the resistor 35a. The transformer 32 has a feedback coil 32c which 
is connected to the base of the transistor 33 through the capacitor 34 and 
the resistor 35. The transformer 32 has the secondary winding 32b grounded 
through the diode 36, a capacitor 37 and the primary winding 38a of an 
ignition coil 38. The ignition coil 38 has the secondary winding 38b 
connected to a spark plug 39. The ignition coil 38 has the primary winding 
38a connected in parallel with a diode 40. Between the junction of the 
diode 36 and the capacitor 37, and the ground is connected a discharge 
control thyristor 41. 
Reference numeral 42 designates a signal coil which generates a signal in 
synchronism with the revolution of an engine (not shown). The signal coil 
is connected to a noninverted terminal of a comparator 44 through a diode 
43. The comparator 44 has an inverted terminal connected to the junction P 
of resistors 45 and 46 which give a reference voltage. The comparator 44 
has an output terminal connected to a noninverted terminal of a comparator 
50 through a delay circuit 49 which comprises a resistor 47 and a 
capacitor 48 to have a predetermined delay time t.sub.1. The delay time 
t.sub.1 is set to be enough to decrease the electromagnetic energy of the 
transformer 32 in a suitable manner. The comparator 50 has an inverted 
terminal connected to the junction P, and an output terminal connected to 
the gate of the thyristor 41 through a resistor 51. 
Reference numeral 52 designates an oscillation stoppage control circuit 
which comprises a comparator 53, a diode 54, a capacitor 55, a resistor 56 
and an oscillation stoppage transistor 57. The comparator 53 has a 
noninverted terminal connected to the output terminal of the comparator 
44. The comparator 53 has an inverted terminal connected to the junction 
P. The comparator 53 has an output terminal grounded through the diode 54 
and the capacitor 55, and also connected to the base of the transistor 57 
through the resistor 56. The transistor 57 has the emitter grounded, and 
the collector connected to the base of the transistor 33 of the power 
circuit. The capacitor 55 and the resistor 56 constitute a time constant 
circuit which has a predetermined delay time t.sub.2. The delay time 
t.sub.2 is set to be enough to be capable of restoring the withstand 
voltage of the thyristor 41 in a suitable manner. The delay circuit 49 and 
the oscillation stoppage control circuit 52 constitute a converter control 
unit. 
Now, the operation of the embodiment shown in FIG. 1 will be described in 
detail in reference to FIG. 2. In FIG. 2, there is shown the collector 
voltage of the transistor 33 at FIG. 2(a). There is shown the output 
voltage of the signal coil 42 at FIG. 2(b). There is shown the voltage 
across the base and the emitter of the transistor 57 at FIG. 2(c). There 
is shown the gate voltage of the thyristor 41 at FIG. 2(d). There is shown 
the charge voltage for the capacitor 37 at FIG. 2(e). 
When the output voltage from the signal coil 42 is 0 or negative, the 
output voltage form the comparators 44 and 53 is 0 because the output 
voltage from the signal coil 42 is lower than the reference voltage at the 
junction P. As a result, the transistor 57 is off, and the transistor 33 
makes self-excited oscillation to repeat on and off as shown at FIG. 2(a), 
causing the converter to be active. Thus, the output voltage from the 
battery 31 is increased to a high level by the transformer 32, and the 
increased voltage is rectified by the diode 36, gradually charging the 
capacitor 37 as shown at FIG. 2(e). 
When the output voltage from the signal coil 42 becomes positive and higher 
than the reference voltage, output voltages appear at the output terminals 
of the comparators 44 and 53. The output voltage of the comparator 53 is 
given to the base of the transistor 57 to generate a voltage across the 
base and the emitter of the transistor 57 as shown at FIG. 2(c), turning 
on the transistor 57. As a result, the transistor 33 is turned off to 
cease its oscillation, causing the converter to be inactive. At that time, 
the collector voltage of the transistor 33 maintains a high level as shown 
at FIG. 2(a). 
On the other hand, the delay circuit 49 delays the output voltage of the 
comparator 44 by the predetermined delay time t.sub.1, and transmits the 
output voltage to the comparator 50. Then the comparator 50 supplies the 
gate of the thyristor 41 with a gate voltage as shown at FIG. 2(d). Thus, 
the thyristor 41 is conducted to discharge the electric charges stored in 
the capacitor 37 through the thyristor and the primary winding 38a of the 
ignition coil 38. This results in the generation of a high voltage at the 
secondary winding 38b of the ignition coil 38, causing the spark plug 39 
to produce a spark. 
Next, when the output voltage of the signal coil 42 becomes lower than the 
reference voltage, the output voltages of the comparators 44 and 53 are 0. 
The electric charges which have been stored in the capacitor 55 are 
discharged through the base to emitter collection of the transistor 57, 
and the voltage across the base and the emitter of the transistor 57 
becomes 0 after the predetermined delay time t.sub.2 as shown at FIG. 
2(d), turning off the transistor 57. As a result, the transistor 33 is 
turned on to restart its oscillation, causing the converter to be active 
again. The operation as stated earlier will be repeated. 
In the embodiment, the oscillation ceases and makes the converter inactive 
earlier than the conduction of the thyristor by the certain time. This 
arrangement prevents a current from flowing through the transformer 32 in 
that time, and the electromagnetic energy stored in the transformer can be 
extinguished in that time. No trouble will occur even if the thyristor 41 
is triggered after that time. In addition, the embodiments has such an 
arrangement in that the oscillation is stopped for the certain time after 
ignition to ensure the full revival of the withstand voltage of the 
thyristor 41 before the oscillation restarts. This arrangement prevents 
the thyristor 41 from continuously conducting. 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein.