Ignition control system with closure angle independent of residual energy stored in ignition coil

The closure angle of an interrupter switch connected in series with the primary winding of an ignition coil is varied as a predetermined function of engine speed by charging and discharging of an integrator circuit which in turn changes the cut-in threshold of a threshold circuit controlling the operation of the interrupter switch. When the spark repetition rate becomes sufficiently high for residual energy to be stored in the coil when the interrupter switch closes, this type of control results in an undesired decrease of closure angle. Therefore, in the present system, the operation of the charging circuit for the integrator circuit is always delayed until the current through the primary winding reaches a predetermined minimum value exceeding the maximum possible residual current in the primary winding when the interrupter switch first closes. The charging circuit thus always operates from the same initial condition, preventing undesired changes in the closure angle at high speeds.

Cross reference to related applications and publications: U.S. Pat. No. 
4,176,645. 
The present invention relates to ignition systems and particularly to 
ignition systems in which the closure angle of an interruptor switch 
connected in series with primary winding of the ignition coil is varied as 
a predetermined function of engine speed. 
BACKGROUND AND PRIOR ART 
An ignition system of the above-described type is disclosed in U.S. Pat. 
No. 4,176,645. In the type of ignition system disclosed therein the 
closure angle varies relatively exactly according to the predetermined 
function as long as the speed of the engine (and the number of cylinders) 
results in an ignition repetition rate which is below a maximum value in 
which residual storage effects in the output stage become noticeable. If, 
however, this maximum value is exceeded, an undesired decrease in the 
closure angle relative to the desired closure angle results for the 
following reasons. In the known system, the closure angle control takes 
place by a charging and discharging of an integrator circuit during the 
time the interrupter switch is closed. Specifically, the charging of the 
integrator starts as the interrupter switch closes and continues until the 
current through the primary winding of the ignition coil reaches a 
predetermined limiting value. At this time a discharge of the integrator 
circuit commences. Above a particular ignition repetition rate, residual 
energy will still be stored in the ignition coil when the interrupter 
switch closes. This causes the current through the interrupter switch to 
jump to a value corresponding to this residual energy when the switch 
closes. The time for the current through the primary winding to reach the 
predetermined limiting value, that is the charging time of the integrator 
circuit is thus decreased, while the discharge time remains the same. The 
final value of voltage across the integrator circuit which in turn 
determines the threshold value of a threshold circuit controlling the 
interrupter switch therefore changes at high engine speeds for a given 
number of cylinders in a direction causing an unwanted decrease in the 
closure angle. 
THE INVENTION 
It is an object of the present invention to prevent the above-mentioned 
undesired decrease in the closure angle. The object of the present 
invention is thus to allow the closure angle to vary as a predetermined 
function of speed throughout the whole speed range of the engine, 
independently of any residual energy stored in the ignition coil. 
In accordance with the present invention, the means which supply DC current 
to the integrator circuit operate only after the current through the 
primary winding reaches a predetermined minimum value which exceeds the 
maximum residual current value present in the primary winding of the 
ignition coil at the highest engine speed. The control of the closure 
angle is achieved by a shifting of the cut-in threshold of a threshold 
circuit which operates the interrupter switch, as in the known circuit, 
but the shift of the cut-in threshold only takes place when the current 
through the primary winding has a predetermined minimum value, thereby 
setting the same initial conditions for the charging of the integrator 
circuit throughout the whole speed range.

The ignition system of FIG. 1 is to be used in an internal combustion 
engine and, more particularly, in an internal combustion engine in a motor 
vehicle. The source of energy is a battery 1, which may be the battery of 
the motor vehicle. The positive terminal of battery 1 is connected through 
an operating switch 2 to the positive supply line 3, while the negative 
terminal of battery 1 is connected to a line 4 which is at reference 
potential. The positive supply line 3 is connected to the negative supply 
line 4 through a series circuit including the primary winding 5 of an 
ignition coil 6, an electronic interrupter switch 7 and a monitoring 
resistor 8. 
In the circuit shown on FIG. 1, the electronic interrupter switch is 
comprised by the emitter-collector circuit of a transistor 7'. The 
collector of transistor 7' is connected to one end of the secondary 
winding 9 of ignition coil 6 whose other end is connected to one terminal 
of a spark plug 10 whose other terminal is connected to reference 
potential. Of course secondary winding 9 of ignition coil 6 may be 
connected to a plurality of spark plugs through a distributor. 
The positive supply line 3 is also connected to the anode of a diode 11 
whose cathode is connected through a voltage divider including resistors 
12 and 13 to the negative supply line. The common point of resistors 12 
and 13 is denoted by reference numeral 14. The potential at circuit point 
14 is approximately half of the battery potential. 
The ignition system includes a threshold switch 15 which, in the example 
shown in FIG. 1, is an operational amplifier having an inverting input 17 
and a direct input 18. A positive feedback resistor 20 is connected 
between output 19 of operational amplifier 16 and its direct input. 
Further, operational amplifier 16 is connected through a line 26 to the 
cathode of diode 11 and through a line 22 to the negative supply line 4. 
The direct input 18 of operational amplifier 16 is connected through a 
matching resistor 23 to circuit point 14. The inverting input 17 of 
operational amplifier 16 is further connected through a pair of resistors 
24, 25 to one side of a timing signal generator 26. The other side of 
timing signal generator 26 is connected to circuit point 14. The common 
point of resistors 24, 25 is connected through a noise filtering capacitor 
27 to circuit point 14. 
Timing signal generator 26, in a preferred embodiment, is an AC generator 
and furnishes an AC voltage which has the shape shown in the voltage (U) 
vs. time (t) diagram of FIG. 2a. The wave shape shown on the left side of 
FIG. 2a corresponds to low engine speeds n.sub.n while that on the right 
side of the figure corresponds to high engine speeds n.sub.h. Inverting 
input 17 is further connected through a resistor 28 to negative supply 
line 4 and through two parallel lines 29, 30 to an integrator 31. 
Integrator 31 is shown as a capacitor. The voltage across capacitor 31 
constitutes a control voltage whose value determines the switch-in 
threshold U2 (FIG. 2a). Interconnected between line 29a and capacitor 31 
is a series circuit including resistance 32 and a diode 33 whose cathode 
is connected to capacitor 31. Interconnected between line 30 and capacitor 
31 is a series circuit including a resistor 34 and a diode 35 whose anode 
is connected to capacitor 31. Resistance 32 includes two resistors 36, 37, 
the common point of resistors 36, 37 being connected to the anode of a 
diode 38 whose cathode is connected to circuit point 14. The common point 
of resistors 36, 37 is further connected through a resistor 39 and a diode 
40 to the collector of a transistor 41. The base of transistor 41 is 
connected through a resistor 42 to the output 19 of operational amplifier 
16 and through a resistor 43 to the cathode of diode 11. Transistor 41 is 
a pnp transistor. Its emitter is connected to the cathode of diode 11. 
Although integrator 31 is shown as being a capacitor it could, of course, 
also be a capacitor used in conjunction with an operational amplifier (not 
shown). 
Integrator 31 is further connected to the collector of a first (pnp) 
control transistor 45 as well as with the collector of a second (npn) 
control transistor 46. The emitter of first control transistor 45 is 
connected through a resistor 47 and its base through resistor 48 to the 
cathode of diode 11, so that a constant current appears in the 
emitter-collector circuit of transistor 45. The above-described network 
therefore constitutes a constant current source. Similarly, the emitter of 
second control transistor 46 is connected through a resistor 49 and its 
base through a resistor 50 to the negative supply line 4, whereby this 
network also constitutes a constant current source. The base of second 
control transistor 46 is connected through a resistor 51 to the anode of a 
blocking diode 52. The cathode of blocking diode 52 is connected to the 
collector of an npn transistor 53 and through a resistor 55 to the base of 
first control transistor 45. The anode of blocking diode 52 is further 
connected through a resistor 56 to the collector of transistor 41. 
Transistor 7' is preferably connected as a Darlington circuit. The common 
point of transistor 7' and monitoring resistor 8 is connected directly to 
the emitter of transistor 53 and that of a further transistor 57. The base 
of transistor 53 is connected through a diode 58 and a resistor 59 to the 
negative supply line, while the base of transistor 57 is connected through 
a diode 60 and a resistor 61 to the negative supply line. The base of 
transistors 53 are connected, respectively, through a resistor 62 and a 
resistor 63 to a circuit point 64. Circuit point 64 is connected through a 
resistor 65 to the cathode of diode 11. Circuit point 64 is further 
connected through a Zener diode 66 to the negative supply line 4. Zener 
diode 66 provides a stabilized voltage for the base voltage dividers 62, 
58, 59 and 63, 60, 61 of transistors 53, 57 respectively. The collector of 
transistor 57 is connected through a resistor 67 to the base of an 
additional transistor 68. The emitter of transistor 68 is directly 
connected to the cathode of diode 11; the collector of transistor 68 is 
connected directly to the base of control transistor 45. 
A series circuit including resistors 69 and 70 is connected in parallel 
with monitoring resistor 8. The common point 71 of resistors 60 and 70 is 
connected through a resistor 72 to the base of a driving transistor 73. 
The base of transistor 73 is connected through a resistor 74 to the 
cathode of diode 11, while the collector of transistor 73 is connected 
thereto through a resistor 75. 
The base of transistor 73 is connected to the output of operational 
amplifier 16 through a resistor 77. The collector of transistor 73 is 
connected to the base of transistor 7' through a diode 84, the anode of 
diode 84 being connected to the collector of transistor 73. Further, the 
cathode of a diode 85 is also connected to the collector of transistor 73. 
Its anode is connected to the emitter of transistor 73. 
As shown in FIG. 2a, the control signal for operating threshold switch 15 
should increase over a period of time relative to the potential at circuit 
point 14 to a peak value U.sub.1 and then should decrease. Thus for the 
present case at least the half wave W1 of the signal furnished by timing 
signal generator 26 which is positive with respect to circuit point 14 can 
be utilized as a control signal. Threshold switch 15 is controlled by 
means of resistor 28 in such away that, during startup of the internal 
combustion engine, switch 15 may be switched in and switched out by the 
positive half wave. Thus, as clearly shown in FIG. 2a, when the internal 
combustion engine first starts up, the cut-in threshold U2 and the cut-out 
threshold U3 of threshold switch 15 are at a level only slightly above the 
zero line of the AC voltage furnished by timing signal generator 26. 
This arrangement has the advantage that when the operating switch 2 is 
closed but the internal combustion engine is at rest, the 
emitter-collector circuit of transistor 7' is definitely in a blocked 
state, so that no current can flow over primary winding 5 of the ignition 
coil. Such a current could lead to excessive heating of ignition coil and 
possibly to its destruction. 
As the internal combustion engine increases in speed, the cut-in threshold 
U2 moves first in the direction of arrow A towards the peak value U.sub.1 
of the positive half wave W1. For further increasing speeds, threshold U2 
moves away from peak value U.sub.1 in the direction of arrow B. The 
shifting of threshold U2 away from peak value U.sub.1 can extend almost 
down to the negative peak value U4 of the signal furnished by timing 
signal generator 26. 
As long as the speed of the internal combustion engine is increasing, the 
cut-out threshold U3 is maintained at its original value until such time 
as the cut-in threshold U2 has reached its original value during its 
movement away from peak value U.sub.1. As soon as the cut-in threshold U2 
has reached its original position, a further increase in the speed of the 
internal combustion engine causes the cut-out threshold U3 to be moved 
jointly with cut-in threshold U2 in the direction of arrow B. 
Specifically, the cut-out threshold will precede the cut-in threshold by 
at least a small amount. 
The shifting of the cut-in threshold U2 takes place as follows. First, when 
the current in the primary winding of the ignition coil reaches a 
predetermined value I.sub.min a first change .DELTA.U.sub.5 of the then 
present integration value U.sub.6 in integrator 31 takes place. The end of 
the first change .DELTA.U.sub.5 and the beginning of a subsequent change 
.DELTA.U.sub.7 takes place when the current in the primary winding 5 of 
the ignition coil has reached a monitoring value I.sub.0. The variation 
with respect to time of primary current in ignition coil 6 is shown in 
FIG. 2b. The end of the second change .DELTA.U.sub.7 is determined by the 
cut-out of threshold switch 15. The value U.sub.9 now stored in integrator 
31 remains there until the next subsequent first change. This maintaining 
of a value stored on a capacitor is particularly readily accomplished by 
the use of an operational amplifier. Preferably, the first change 
.DELTA.U.sub.5 and the second change .DELTA.U.sub.7 are so adjusted that, 
when the speed of the internal combustion engine remains constant, the 
changes are symmetrical relative to a perpendicular E drawn through the 
value U.sub.8, namely the value at the end of the change .DELTA.U.sub.5 
and at the start of the change .DELTA.U.sub.7. The change from 
.DELTA.U.sub.5 to .DELTA.U.sub.7 is determined by choice of the monitored 
current I.sub.0. After the value of current I.sub.0 is reached, the 
current in the primary winding is allowed to increase until it reaches a 
value I.sub.1 for which a sufficient energy for ignition is stored in 
ignition coil 6. 
In the present case, the changes .DELTA.U.sub.5 and .DELTA.U.sub.7 are 
achieved by DC currents of opposite polarity, the DC current causing the 
change .DELTA.U.sub.5 having a higher level as will be explained in 
greater detail below. 
Finally, it should be noted that the voltage at output 19 of threshold 
switch 15, which is shown in FIG. 2e and whose cut-in and cut-out 
thresholds are shown in FIG. 2d, should be a potential U.sub.10 when 
threshold switch 15 is cut off, that is in the time interval between 
t.sub.1 and t.sub.2. Potential U.sub.10 should be substantially equal to 
the potential of the positive supply line 3. Similarly, the potential 
U.sub.11 at output 19 when threshold switch 15 is cut in, that is in the 
time interval between t.sub.2 and t.sub.3, should be at least 
approximately equal to that on the negative supply line 4. 
OPERATION 
As soon as the voltage furnished by timing signal generator 26 reaches the 
cut-in threshold value U.sub.2 following closure of operating switch 2, 
the potential U.sub.11 appears at the output 19 of the switch. As 
mentioned above, this potential is approximately equal to that of the 
negative supply line 4. This causes transistor 41 to be switched to the 
conductive state through the base voltage divider 42, 43. Simultaneously, 
transistor 73 is blocked so that sufficient base current can now flow over 
resistor 75 and diode 84 to transistor 7', causing the latter to become 
conductive. Current starts to flow through primary winding 5, the 
collector-emitter circuit of transistor 7' and monitoring resistor 8. 
As mentioned above, the cut-in threshold U.sub.2 at the start of the engine 
is only a short value away from the zero line, that is only slightly above 
the potential at circuit point 14, so that threshold switch 15 will be 
reliably switched in even during the start-up of the engine. 
As soon as the current through primary winding 5 reaches a predetermined 
minimum value I.sub.min, which causes a corresponding voltage drop across 
monitoring resistor 8, transistor 57 which was previously conductive 
becomes blocked and blocks transistor 68. This causes transistor 45 to be 
switched to the conductive state so that a constant DC current flows over 
resistor 47 and the emitter-collector circuit of transistor 45 to 
integrator 31 (i.e. capacitor 44). This causes the first change 
.DELTA.U.sub.5 to take place across integrator 31. This change ends as 
soon as the current through primary winding 5 reaches the monitoring value 
I.sub.0. At this point the voltage drop across resistor 8 has a value at 
which transistor 53 is switched to the blocked state. This causes 
transistor 45 to block and transistor 46 to be switched to the conductive 
state, since its base-emitter circuit now receives current through the 
emitter-collector circuit of transistor 41. Since the emitter-collector 
circuit of transistor 46 is now conductive, the second change 
.DELTA.U.sub.7 takes place, starting at the value U.sub.8 present at the 
beginning of the blocking of transistor 45. The second change, 
.DELTA.U.sub.7, ends as soon as the signal furnished by timing signal 
generator 26 reaches the cut-out threshold U.sub.3 of switch 15. 
Thereafter the potential U.sub.10 appears at output 19 of threshold switch 
15, this potential being approximately equal to the potential of the 
positive supply line 3. The change in potential at the output of threshold 
switch 15 at time t.sub.2 causes transistor 41 to block. Current no longer 
flows over the base-emitter circuit of transistor 41, causing its 
emitter-collector circuit to switch to the blocked state. This cuts off 
the current for the base-emitter circuit of transistor 46 causing its 
emitter-collector circuit to become blocked. This ends the second change 
.DELTA.U.sub. 7 at integrator 31. The jump in potential at the output of 
threshold switch 15 causes base current to be supplied to transistor 73 
through resistor 77. Transistor 73 switches to the conductive state 
causing base current to be shunted away from transistor 7'. Transistor 7' 
blocks, interrupting the current through the primary winding 5 of ignition 
coil 6. The interruption of current causes a high voltage to be induced in 
secondary winding 9, which causes a spark to be generated at spark plug 
10. 
In the ignition system of FIG. 1, transistor 73 further functions to 
prevent further increases in the current through the primary winding 5 of 
ignition coil 6 after it has reached a predetermined value I.sub.1 
required for proper ignition. Specifically, when the voltage across 
resistor 8 reaches a value corresponding to the current I.sub.2, the 
voltage at circuit point 71 as determined by resistor 69 causes the 
conductivity of transistor 73 to increase so that transistor 7' no longer 
receives full base current and therefore decreases the current through 
primary winding 5 to the predetermined value I.sub.1. The circuit for 
limiting the primary current should be so designed that, when the internal 
combustion engine starts up, the current through the primary winding 5 
will remain at the value I.sub.1 for a time interval (t.sub.2 ' to 
t.sub.3) so that during acceleration of the vehicle driven by the internal 
combustion engine enough ignition energy will be stored in the ignition 
coil in spite of the shortening of the time during which current flows. 
When the engine first starts up, the second change .DELTA.U.sub.7 takes 
place over a longer time interval than the first change .DELTA.U.sub.5, so 
that the final value U.sub.9 stored in the integrator after the second 
change .DELTA.U.sub.7 is always more negative than was the value U.sub.6 
prior to the first change .DELTA.U.sub.5. Because of the presence of the 
circuit connected to line 29 (36, 37, 33) this affects the inverting input 
17 in such a way that the cut-in threshold U.sub.2 of the switch changes 
in a positive direction (arrow A). As the speed of the internal combustion 
engine increases, the second change .DELTA.U.sub.7 taking place at 
integrator 31 will extend over a smaller time interval than the first 
change .DELTA.U.sub.5, so that the integration value U.sub.9 following the 
second change .DELTA.U.sub.7 will be more positive than the integration 
value U.sub.6 prior to the first change .DELTA.U.sub.5. This, in turn, 
affects the inverting input 17 (via the circuit connected to line 29, and, 
after the integration value U.sub.9 is positive, relative to circuit point 
14 through the circuit connected to line 30), in such a way that the 
threshold U.sub.2 changes in the negative direction (arrow B). It should 
be noted that the circuit connected to line 30 (34, 35) is of lower 
resistance than the circuit connected to line 29. Thus, when the engine 
first starts up, the primary winding 5 receives sufficient current to 
allow proper ignition, the current limiting circuit including transistor 
73 becoming effective and transistor 7' being temporarily in an active 
state, that is having relatively high losses. This, however, only occurs 
in a speed region of the engine which immediately follows startup and ends 
very rapidly. The undesirable losses are compensated for by the fact that 
the shifting of the cut-in threshold U.sub.2 of threshold switch 15 from 
the region of the peak value U.sub.1 of the positive half wave into the 
region of the peak value U.sub.4 of the negative half wave W2 allows a 
relatively constant energy to be stored in ignition coil 6 up to a 
relatively high engine speed. 
When transistor 41 switches to the conductive state, the circuit including 
diode 40, resistor 39 and diode 38 becomes effective, causing the common 
point of resistors 36, 37 to be approximately at the potential of circuit 
point 14 when threshold switch 15 is switched in. Changes in the value 
stored on integrator 31 therefore do not affect threshold switch 15. The 
cut-out value U.sub.3 of threshold switch 15 therefore has a stabilized 
value as long as the cut-in threshold value U.sub.2 moves in the region 
between its original position and the peak value U.sub.1 of positive half 
wave W1. Integrator 31 thus cannot have any deleterious effect on the 
ignition timing. At higher engine speeds this stabilization is no longer 
required, because a relatively rapid decrease of AC voltage from the peak 
value U.sub.1 then takes place. 
On the other hand, for high engine speeds, the time in which transistor 7' 
is blocked can be so short that a residual storage effect results. Since 
energy would then still be stored in ignition coil 6 when transistor 7' 
again becomes conductive, the primary winding through the ignition coil 
would jump to a value which is higher than zero. This in turn would result 
to an undesired shortening of the time during which the first change 
.DELTA.U.sub.5 occurs. In order to prevent this, the first change 
.DELTA.U.sub.5 in accordance with the present invention is only carried 
out after the current through the primary winding has reached a minimum 
value I.sub.min, the value I.sub.min being higher than the maximum 
starting current to be expected through primary winding 5. Thus definite 
starting conditions for change .DELTA.U.sub.5 are established and the 
above-mentioned undesired shortening of the closure time is prevented. 
The present invention need not be limited to the example shown in the 
drawing. The same principle can be applied to different types of ignition 
systems for example those without .alpha..sub.s control as, for example, 
ignition systems with Hall generators. In that case the voltage would be 
used to control a timing stage. 
Various changes and modifications may be made within the scope of the 
inventive concepts.