Ignition system

The present invention is an ignition device comprising a circuit for generating an ignition signal in synchronism with the revolutions of an engine, a circuit for inhibiting an igniting operation, a circuit for detecting the starting state of the engine, and a circuit for interrupting the operation of the inhibiting circuit upon detection of such starting state.

FIELD OF THE INVENTION 
The present invention relates to an ignition device comprising a circuit 
for generating an ignition signal in synchronism with the revolutions of 
an engine, a circuit for inhibiting an igniting operation, a circuit for 
detecting the starting state of the engine, and a circuit for interrupting 
the operation of the inhibiting circuit upon detecton of such starting 
state.

BACKGROUND OF THE INVENTION 
FIG. 1 is a circuit diagram showing a prior art capacitor discharge type 
ignition device. A terminal 1 is connected with the output terminal of an 
a.c. generator which is mounted on a vehicle. An a.c. voltage fed to 
terminal 1 is rectified by a diode 2 and is supplied to a capacitor 3. The 
latter is charged on the basis of that rectified voltage. Between the plus 
terminal 4 of capacitor 3 and the ground, there is connected in a forward 
direction a thyristor 5 which has its gate terminal connected with the 
output terminal of a gate signal generator 6. A pulse signal concerning 
the ignition timing is inputted to the input terminal 7 of gate signal 
generator 6. Between the gate terminal of thyristor 5 and the ground, 
moreover, there is connected an npn type transistor 8 which has its base 9 
connected with the output terminal of an r.p.m. detector 10 made receptive 
of the output signal of the aforementioned gate signal generator 6 for 
detecting a predetermined r.p.m. of the engine. On the other hand, the 
primary coil 12a of an ignition coil 12 is connected between the minus 
terminal 11 of capacitor 3 and the ground, and an ignition plug 13 is 
connected between the insulated terminal of the secondary coil 12b of 
ignition coil 12 and the ground. 
When gate signal generator 6 outputs a positive pulse to capacitor 3 
charged, according to the construction described above, thyristor 5 is 
rendered conductive so that a discharge current flows, as indicated by 
broken lines A. As a result, a high voltage is induced in secondary coil 
12b to ignite ignition plug 13. As a result of repetitions of the charge 
of capacitor 3 and the generation of the positive pulses of gate signal 
generator 6, periodic ignitions are continued in ignition plug 13 to 
effect the igniting operation. 
At the start of the engine, however, backward torque may be generated in 
the engine if the starting r.p.m. of the engine is inadequate. In order to 
prevent this, the weight of the engine is increased in order to enhance 
its strength. 
In view of this, according to the prior art, a signal for turning on the 
transistor 8 is outputted, when the r.p.m. detected by the r.p.m. detector 
10 is no greater than a predetermined value, to ground the gate terminal 
of thyristor 5 through transistor 8. for this purpose, thyristor 5 is held 
inconductive to inhibit the igniting operation of the ignition plug 13. 
In case a starter motor is to be used for starting the engine which is 
equipped with the ignition device having the above-specified construction, 
ignition plug 13 is not able to perform its igniting operation, therby to 
leave the engine start impossible, unless the engine r.p.m. is increased 
to exceed the predetermined value. This unnecessarily results in an 
increase in the output of the starter motor and in the capacity of the 
battery. As a result, these devices must have their sizes and weights 
enlarged. 
SUMMARY OF THE INVENTION 
In the ignition device for inhibiting the igniting operation to block the 
generation of the backward torque of the engine when the engine r.p.m. is 
small, the present invention contemplates to release the inhibition of the 
starting operation only at the start of the engine, thereby to make the 
igniting operation possible from a small r.p.m. so that the size of the 
starter motor and the capacity of the battery may be reduced. 
DETAILED DESCRIPTION 
With a terminal 1, as shown in FIG. 2, there is connected the output 
terminal of an a.c. generator which is attached to the engine of a 
vehicle. Reference numeral 15 indicates the a.c. generator as an a.c. 
power supply. An a.c. voltage signal fed to the terminal 14 from the a.c. 
generator 15 is rectified by a diode 16 and is then supplied to a 
capacitor 17. The capacitor 17 is caused to conduct its charging operation 
by the voltage supplied thereto. 
Reference numeral 18 indicates a rotor which is formed with a projection 
18a and which is made of a ferromagnetic material. The rotor 18 is made 
rotatable with the crankshaft (not shown) of the engine. In the vicinity 
of the rotor 18, there is arranged an electromagnetic pickup 19 which has 
its magnetic core 20 wound by a pulser coil 21 and which is biased by a 
permanent magnet 22. When the rotor 18 revolves in the direction of the 
arrow so that its projection 18a passes over the front of the magnetic 
core 20 of the electromagnetic pickup 19, there is generated at the output 
terminal of the pulser coil 21 a signal S.sub.1 which is synchronized with 
the revolutions of the engine. 
Reference numeral 23 indicates a gate signal generator which is made 
receptive of the aforementioned signal S.sub.1 synchronized with the 
engine revolutions to output an ignition signal S.sub.2 which is composed 
of a positive pulse signal corresponding to the ignition timing. Between 
the plus terminal 24 of the aforementioned capacitor 17 and the ground, on 
the other hand, there is connected a thyristor 25 which is directed 
forward to the ground. The output terminal of the gate signal generator 23 
is connected with the gate terminal of the thyristor 25. Moreover, an npn 
type transistor 26 is connected between the gate terminal of the thyristor 
25 and the ground. Numeral 27 indicates an r.p.m. detector which has its 
output terminal connected with the base of the transistor 26. The r.p.m. 
detector 27 is made receptive of the output signal S.sub.2 of the 
aforementioned gate signal generator 23 to apply an output signal for 
turning off the transistor 26 to the base of the transisitor 26 when the 
engine r.p.m. becomes equal to or smaller than a predetermined value 
smaller than the idling value. 
Next, reference numeral 28 indicates a battery which is mounted on the 
vehicle. Between the anode of the battery 28 and the ground, there are 
connected in series a starter switch 29 and an exciting oil 30a of a relay 
switch 30, and a normally open relay contact 30b of the relay switch 30 
and a starter motor 31. Between the base of the aforementioned transistor 
26 and the ground, on the other hand, there is connected an npn type 
transistor 32 having a base and an emitter, between which is connected a 
parallel circuit composed of a resistor 33 and a capacitor 34. Moreover, 
the earthed terminal of the starter switch 39 and the base of the 
transistor 32 are connected through a diode 35. 
Moreover, reference numeral 36 indicates an ignition coil which has its 
primary coil 36a connected between the minus terminal of the capacitor 17 
and the ground. An ignition plug 37 is connected with a high-voltage 
terminal of a secondary coil 36b and the ground. 
With the construction thus far described, while the engine is running, the 
a.c. voltage signal outputted from the a.c. generator 15 is rectified to 
charge the capacitor 17. When the engine r.p.m. is not smaller than the 
value which is predetermined by the r.p.m. detector 27, the transistor 26 
is in its off state. As a result, the ignition signal S.sub.2 outputted 
from the gate signal generator 23 on the basis of the signal S.sub.1 
outputted from the pulser coil 21 is supplied to the gate terminal of the 
thyristor 25 to periodically render the thyristor 25 conductive in 
synchronism with the revolutions of the engine. Each time the thyristor 25 
is rendered conductive, the capacitor 17 is discharged to induce a high 
voltage in the secondary coil 36b of the ignition coil 36 so that ignition 
plug 37 sparks. 
When the engine r.p.m. is not larger than the predetermined value set by 
the r.p.m. detector 27, the transistor 26 is turned on to earth the gate 
terminal of the thyristor 25 to the ground. In this case, therefore, the 
thyristor 25 is left inconductive even if the gate signal generator 23 
outputs the ignition signal S.sub.2. As a result, the discharge of the 
capacitor 17 is blocked so that the ignition plug 37 does not spark. Thus, 
when the engine r.p.m. is equal to or smaller than the predetermined value 
set by the r.p.m. detector 27, the igniting operation of the ignition plug 
37 can be inhibited to prevent backward torque of the engine from being 
established. 
When starter switch 29 is turned on for starting the engine to run the 
starter motor 31, the existing coil 30a is energized, so that the relay 
contact 30b is closed to supply the starter motor 31 with electric power. 
At this time, the current supplied from the battery 28 is adjusted to have 
a predetermined voltage through the diode 35, and is applied to the base 
of the transistor 32 to turn on the transistor 32. When transistor 32 is 
turned on, the base of the transistor 26 is earthed to the ground so that 
the transistor 26 can be held inconductive even if the r.p.m. detector 27 
outputs its output signal. As a result, at the start of the engine by the 
starter motor 31, the thyristor 25 can be turned on or off by the ignition 
signal outputted from the gate signal generator 23, even in case the 
engine r.p.m. is smaller than the value set by the r.p.m. detector 27. 
Thus, the capacitor 17 is enabled to conduct its charging and discharging 
operations so that the ignition plug 37 is allowed to perform its igniting 
operation. 
After the start of the engine is completed, the starter switch 29 is turned 
off to render the transistor 32 inconductive. As a result, the conductive 
and inconductive states of the transistor 26 restore the aforementioned 
normal state which is controlled by the output signal of the r.p.m. 
detector 27. 
At the start of the engine, as has been described above, the operation of 
the circuit composed of the r.p.m. detector 27 and the transistor 26 for 
inhibiting the ignition operation is interrupted. As a result, the 
ignition circuit can be run at a remarkably small r.p.m. even at the start 
of the engine, so that the engine can be started even by a small-sized 
starter motor and a small-capacity battery. 
It will be clear from the foregoing description that, according to the 
present invention, the structure for making the operation of the igniting 
operation inhibiting circuit impossible at the engine start is added to 
the ignition device which is constructed to inhibit the igniting operation 
when the engine r.p.m. is at a low value satisfying the predetermined 
conditions. As a result, the igniting operation at low r.p.m. is made 
possible only at the engine start to drop the r.p.m. of the starter motor 
necessary for starting the engine to permit reduction of the size of the 
starter motor and the capacitor of the battery mounted on the vehicle.