Contactless ignition control system with a dwell time control circuit for an internal combustion engine

In a contactless ignition control system having a dwell time control circuit for an internal combustion engine, there is provided a speed responsive bias voltage circuit, a bias voltge switching circuit and a wave shaping circuit. The speed responsive bias voltage changes the switching level of the wave shaping circuit, thereby elongating the dwell time of the current flowing through an ignition coil. In the dwell time control, when the ignition timing comes, the bias voltage switching circuit prevents application of the speed responsive bias voltage so that the ignition timing is made irrespective of the speed responsive bias voltage.

BACKGROUND OF THE INVENTION 
The present invention relates to an improvement in a contactless ignition 
system having a dwell time control circuit for an engine such as disclosed 
in Japanese patent publication, Sho 41-2803, published on Feb. 22, 1966, 
assigned to the same assignee of the present application. 
In the above Japanese patent publication, there is shown an ignition 
control system having a dwell time control circuit which comprises an AC 
generator for generating an alternating current signal having timed 
relationship with the engine. Such signal is shown in (a) of FIG. 1 of the 
present application in which an engine speed responsive bias voltage 
changing circuit for generating speed responsive DC signal, as designated 
by V.sub.O (low speed) and V.sub.O ' (high speed) in (a) of FIG. 1 of the 
present application, a waveshaping circuit for generating a rectangular 
control signal and a switching circuit for controlling charge and 
discharge of an ignition coil in response to the rectangular control 
signal. The waveshaping circuit is so arranged that the width of the 
rectangular signal thereof is made longer in accordance with the engine 
speed responsive DC voltage as the engine speed increases, as shown in (b) 
and (c) of FIG. 1 of the present application. As a result, the portion of 
each alternating cycle during which the ignition coil is energized is 
increased as the engine speed increases, thereby ensuring a good 
igniteability of the engine even in the high speed range-thereof. 
However, it has been found to be a drawback that the ignition timing at 
which the discharge of the ignition energy is made is changed with the 
change of the speed responsive DC voltage as designated by T in (c) of 
FIG. 1 of the present application. This time difference T varies with 
variation in the wave shape of the AC voltage due to the type, 
construction, and other characteristics of the AC generator. The 
difference T also depends on variations in the dwell time requirement and 
in manufacturing errors of the igniton system. Generally, the ignition 
timing is made advanced in a high speed range of the engine by spark 
advance mechanisms such as a centrifugal advancer and a vacuum advancer. 
However, it is practically difficult to accurately compensate such time 
difference T by those mechanisms. 
SUMMARY OF THE INVENTION 
It is, therefore, the main object of the present invention to provide an 
engine ignition control system with an improved dwell time control 
function. 
It is another object of the present invention to provide an ignition 
control system which comprises means for selectively applying speed 
responsive DC voltage to the waveshaping circuit in the manner that the 
ignition timing is made at a constant DC voltage with the dwell time being 
elongated as engine speed increases. 
The above and other objects will be made apparent in the following 
description and drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A preferred embodiment will be explained with reference to FIGS. 2 and 3. 
Numeral 1 shows an AC generator which provides an alternating current 
signal as shown in (a) of FIG. 3 in timed relationship with an engine. A 
zener diode 9 provides a constant DC voltage, e.g. 7 volts in cooperation 
with a resistor 10 which is connected to a battery 11. A series circuit of 
a resistor 12 and a transistor 13 is connected at its one end to the zener 
diode 9 and at the other end to a capacitor 14, which is connected across 
the AC generator 1. The emitter and base of the transistor 13 is connected 
to each other in order to provide a diode function having the same 
temperature characteristics as a transistor 29 of a waveshaping circuit 5, 
which will be explained later. The capacitor 14 and other capacitors 15 
and 16 are effective to prevent malfunction of the system. On this 
occasion, diodes 17, 18 and 19 are explained; these diodes are 
respectively connected to prevent the backward biasing. A bias voltage 
changing circuit 2 which is connected to the AC generator 1 comprises a 
rectifying and smoothing circuit 2 including a diode 21, resistor 22 and a 
capacitor 26 and a current amplifying transistor 27 with resistors 23, 24 
and 25 and a thermistor 28 being connected thereto. The thermistor 28 
compensates variation in the temperature responsive characteristics of the 
diode 21 and transistor 27. The bias voltage changing circuit 2 provides 
an engine speed responsive DC voltage signal which increases as the engine 
speed increases. Numerals 3 and 4 show resistors respectively connected to 
the AC generator 1 and the bias voltage changing circuit 2. The previously 
mentioned waveshaping circuit 5 comprises transistors 29 and 30 and 
resistors 31, 32 and 33. The base of the transistor 29 is connected 
through the resistor 3 to the base of the transistor 13. When a DC voltage 
exceeding a predetermined switching value is applied to the base of the 
transistor 29, the transistor 29 is made conductive and, thus, the 
transistor 30 is made nonconductive, thereby providing a rectangular 
signal at the junction of the resistor 33 and the collector of the 
transistor 30. The switching level of the transistor 29 is preferably 
determined to be nearly zero volt by the resistors 12, 3 and 31. Connected 
to the junction is a transistor 36 of a switching circuit 6, which further 
comprises resistors 34 and 35 connected in series with the transistor 
emitter-collector path, a Darlington transistor circuit 37 and surge 
voltage protecting zener diodes 38, 39, 40 and 41. When the rectangular 
signal is generated by the waveshaping circuit 5, the transistor 36 is 
made conductive to thereby render the Darlington transistor circuit 37 to 
be nonconductive. On the other hand, the Darlington circuit 37 is made 
conductive when the rectangular signal disappears. Numeral 7 designates an 
ignition coil having a primary winding connected to the Darlington circuit 
37 and a secondary winding connected to spark plugs as represented by 
numeral 8 in FIG. 2 through a ignition distributor (not shown) in the well 
known manner. The ignition coil 7 is charged with an electric current 
supplied through a resistor 50 from the battery 11 when the Darlington 
transistor 37 is made conductive. 
Now, a bias voltage switching circuit 48 will be explained. This circuit 48 
comprises a differentiating circuit including a capacitor 42, a resistor 
43 and a switching circuit including resistors 44 and 45 and transistors 
46 and 47. A diode 49 is connected between the base circuit of the 
transistor 29 and the transistor 47 of the bias voltage switching circuit 
48 so as to prevent the current flowing through the resistor 3 from 
flowing to the ground when the transistor 47 is made conductive. When a 
voltage decreasing signal is applied to the bias voltage switching circuit 
48 through the capacitor 42, the transistor 46 is made nonconductive to 
render the transistor 47 to be conductive, thereby grounding the output 
signal of the bias voltage changing circuit 2. 
In operation, when the engine speed is low, the AC voltage generated by the 
AC generator 1 is not sufficient to charge the capacitor 26 to the voltage 
to render the transistor 27 to be conductive, and the bias voltage of the 
transistor 29 is not effected by the bias voltage changing circuit 2 but 
is maintained at the level designated by V.sub.O in (a) of FIG. 3. As a 
result, the ignition coil is charged when the AC signal increases to the 
voltage level V.sub.O from the minimum voltage and is discharged when it 
decreases to the level V.sub.O from the maximum in a conventional manner 
as shown in (b) of FIG. 1. 
When the engine speed increases, the capacitor 26 is increasingly charged 
to the voltage to render the transistor 27 to be conductive. As a result, 
the base current is supplied to the transistor 29 increasingly as the 
engine speed increase through the diode 49, the resistor 3, the transistor 
27 and the resistor 25 when the transistor 47 of the bias voltage 
switching circuit 48 is in the nonconductive state. The differentiating 
circuit of the bias voltage switching circuit 48 provides on the base of 
the transistor 46 the voltage shown in (b) of FIG. 3, which is the 
differentiated result of the AC voltage generated by the AC generator 1, 
and, consequently, the switching transistor 47 is made conductive and 
nonconductive as shown in (c) of FIG. 3. As a result, when the AC signal 
in decreasing direction reaches the voltage level V.sub.O the transistor 
29 is made nonconductive since the output current of the bias voltage 
changing circuit 2 is bypassed through the transistor 47 being conductive. 
Consequently, the Darlington circuit 37 switches off the current flowing 
through the ignition coil 7, thereby discharging the ignition energy 
irrespective of the output voltage of bias voltage changing circuit 2. On 
the other hand, when the AC signal turns into the increasing direction 
from its minimum, the transistor 29 is made conductive at the level 
V.sub.O ' since the switching transistor 47 of the bias voltage switching 
circuit 48 is rendered to be nonconductive by the differentiating circuit 
and the base potential of the transistor 29 is raised by the battery 
voltage in the manner as previously mentioned, and consequently the 
Darlington circuit 37 is made conductive relatively earlier than when the 
base potential of the transistor 29 is not raised by bias voltage changing 
circuit 2, thereby to elongate the dwell time of the current supplied to 
the ignition coil, as shown in (d) of FIG. 3. 
In the above preferred embodiment, although the ignition timing is set in 
the decreasing direction of the AC signal, it may be set in the increasing 
direction of the AC signal. In such a modified system, the speed 
responsive DC signal is bypassed through the transistor 47 when the AC 
signal is in the increasing direction. 
It is also possible that the bias voltage switching circuit 48 is connected 
in series with the bias voltage changing circuit 2 and the waveshaping 
circuit 5, and that the switching circuit interrupts application of the 
speed responsive DC voltage to the waveshaping circuit 5 upon the ignition 
timing.