U.S. patent number 3,906,919 [Application Number 05/463,692] was granted by the patent office on 1975-09-23 for capacitor discharge ignition system with controlled spark duration.
This patent grant is currently assigned to Ford Motor Company. Invention is credited to Joseph R. Asik, Mitsugu Hanabusa.
United States Patent |
3,906,919 |
Asik , et al. |
September 23, 1975 |
Capacitor discharge ignition system with controlled spark
duration
Abstract
A capacitor discharge ignition system for a spark-ignition
internal combustion engine. The ignition system includes an
ignition coil having first and second primary windings, a secondary
winding and a ferromagnetic core about which the windings are
wound. A spark plug has electrodes which are spaced apart to form a
spark gap which is connected in series with a first capacitor. The
series-connected spark gap and first capacitor are connected across
the secondary winding. A second capacitor is coupled to the first
winding and a DC source of electrical energy is provided. First
circuit means charge the second capacitor from the DC source and
discharge this capacitor through the first primary winding in timed
relation to operation of the engine. Second circuit means are
provided for producing a fixed frequency oscillatory current in the
second primary winding for a predetermined time interval subsequent
to each discharge of the second capacitor through the first primary
winding. The discharge of the second capacitor through the first
primary winding and the subsequent supply of fixed frequency
oscillatory current to the second primary winding causes
ferroresonant oscillations in the secondary circuit of the ignition
coil for at least a portion of the aforementioned predetermined
time interval. The spark which occurs between the spark plug
electrodes exists during the predetermined time interval and has a
duration which may be varied as desired.
Inventors: |
Asik; Joseph R. (Bloomfield
Hills, MI), Hanabusa; Mitsugu (Ann Arbor, MI) |
Assignee: |
Ford Motor Company (Dearborn,
MI)
|
Family
ID: |
23840980 |
Appl.
No.: |
05/463,692 |
Filed: |
April 24, 1974 |
Current U.S.
Class: |
123/598; 123/596;
123/621; 315/209CD; 123/606 |
Current CPC
Class: |
F02P
3/01 (20130101); F02P 3/0884 (20130101) |
Current International
Class: |
F02P
3/08 (20060101); F02P 3/01 (20060101); F02P
3/00 (20060101); F02p 003/06 () |
Field of
Search: |
;123/148E,148OCD
;315/29CD |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Myhre; Charles J.
Assistant Examiner: Cangelosi; Joseph
Attorney, Agent or Firm: Brown; Robert W. Zerschling; Keith
L.
Claims
Based on the foregoing description of the invention, what is
claimed is:
1. In combination with an internal combustion engine, a capacitor
discharge ignition system, which comprises:
an ignition coil having first and second primary windings, a
secondary winding and a ferromagnetic core about which said
windings were wound;
a spark plug having electrodes spaced to form a spark gap, one of
said electrodes being coupled to one terminal of said secondary
winding;
a first capacitor connected in series with said spark gap, one
terminal of said first capacitor being coupled to the other
terminal of said secondary winding;
a second capacitor coupled to said first primary winding;
a DC source of electrical energy;
first circuit means, coupled to said second capacitor and to said
first primary winding, for charging said second capacitor from said
DC source of electrical energy and for discharging said second
capacitor through said first primary winding in timed relation to
operation of said engine;
second circuit means, coupled to said second primary winding, for
producing an oscillatory current in said second primary winding for
a predetermined time interval subsequent to each discharge of said
second capacitor through said first primary winding;
the discharge of said second capacitor through said first primary
winding and the subsequent production of said oscillatory current
in said second primary winding producing, for at least a portion of
said predetermined time interval, a voltage in the secondary
circuit of ignition coil which oscillates at a frequency defined by
the expresion f = V.sub.m /4N.sub.s .PHI..sub.s where V.sub.m is
the instantaneous maximum voltage across said first capacitor,
N.sub.s is the number of turns in said secondary winding, and
.PHI..sub.s is the magnetic flux within said secondary winding when
said ferromagnetic core of said ignition coil is magnetically
saturated.
2. An ignition system according to claim 1 where said first circuit
means includes means for generating a gating signal for causing the
discharge of said second capacitor through said first primary
winding and wherein said second circuit means includes an
oscillator for generating an oscillatory signal and an amplifier
means for amplifying said oscillatory signal, said amplifier means
being coupled to said second primary winding to produce said
oscillatory current in said second primary winding, said oscillator
being controlled by said gating signal generated by said first
circuit means.
3. An ignition system according to claim 2 wherein said means for
generating said gating signal includes a second oscillator, said
second oscillator being triggered in timed relation to operation of
said engine, said second oscillator having an output signal from
which said gating signal is derived and which determines said
predetermined time interval.
4. In combination with an internal combustion engine, a capacitor
discharge ignition system, which comprises:
an ignition coil having first and second primary windings, a
secondary winding and a ferromagnetic core about which said
windings are wound;
a spark plug having electrodes spaced to form a spark gap, one of
said electrodes being coupled to one terminal of said secondary
winding;
a first capacitor connected in series with said spark gap, one
terminal of said capacitor being coupled to the other terminal of
said secondary winding;
a second capacitor coupled to said first primary winding;
a DC source of electrical energy;
first circuit means, coupled to said second capacitor and to said
first primary winding, for charging said second capacitor from said
DC source of electrical energy and for discharging said second
capacitor through said first primary winding in timed relation to
operation of said engine;
second circuit means for producing an alternating current through
said spark gap subsequent to each discharge of said second
capacitor through said first primary winding, said alternating
current having a frequency f defined by the expression f = V.sub.m
/4N.sub.s .PHI..sub.s where V.sub.m is the instantaneous maximum
voltage across said first capacitor, N.sub.s is the number of turns
in said secondary winding and .PHI..sub.s is the magnetic flux
within said secondary winding when said ferromagnetic core of said
ignition coil is magnetically saturated.
5. An ignition system according to claim 4 wherein said second
circuit means includes an oscillator controlled by said first
circuit means, said oscillator being coupled to said second primary
winding to cause an oscillatory current to flow through said second
primary winding subsequent to each discharge of said second
capacitor through said first primary winding.
6. An ignition system according to claim 5 wherein said alternating
current through said spark gap, during at least a portion of the
the time it exists, has a frequency equal to the frequency of said
oscillatory current in said second primary winding.
7. An ignition system according to claim 6 wherein said alternating
current through said spark gap has a frequency greater than 17
KHz.
8. An ignition system according to claim 6 wherein said oscillator
has an output frequency in the range from 17 to 35.7 KHz.
9. In combination with an internal combustion engine, a capacitor
discharge ignition system, which comprises:
an ignition coil having a primary winding, a secondary winding and
a ferromagnetic core about which said windings are wound;
a spark plug having electrodes spaced to form a spark gap, one of
said electrodes being coupled to one terminal of said secondary
winding;
a first capacitor connected in series with said spark gap, one
terminal of said first capacitor being coupled to the other
terminal of said secondary winding;
a second capacitor coupled to said primary winding;
a DC source of electrical energy;
a first circuit means, coupled to said second capacitor and to said
primary winding, for charging said second capacitor from said DC
source of electrical energy and for discharging said second
capacitor through said primary winding in timed relation to
operation of said engine;
second circuit means, coupled to said primary winding, for
producing an oscillatory current in said primary winding for a
predetermined time interval subsequent to each discharge of said
second capacitor through said primary winding;
the discharge of said second capacitor through said primary winding
and the subsequent production of said oscillatory current in said
primary winding producing, for at least a portion of said
predetermined time interval, a voltage in the secondary circuit of
ignition coil which oscillates at a frequency defined by the
expression f = V.sub.m /4N.sub.s .PHI..sub.s where V.sub.m is the
instantaneous maximum voltage across said first capacitor, N.sub.s
is the number of turns in said secondary winding, and .PHI..sub.s
is the magnetic flux within said secondary winding when said
ferromagnetic core of said ignition coil is magnetically saturated.
Description
BACKGROUND
This invention relates to a capacitor discharge ignition system for
a spark-ignition internal combustion engine. More particularly, it
relates to a ferroresonant capacitor discharge ignition system
which produces a spark discharge in the gap of a spark plug. The
spark discharge is of controllable duration and is characterized by
alternating current flow in the spark gap and a sustained
alternating voltage in the secondary circuit of an ignition coil.
This voltage oscillates at a ferroresonant frequency. The present
invention is related to our commonly assigned patent application
Ser. No. 463,919 filed Apr. 24, 1974 and entitled "Ferroresonant
Capacitor Discharge Ignition System."
Our copending patent application identified above relates to a
capacitor discharge ignition system which has an ignition coil with
a primary winding and a secondary winding wound about a
ferromagnetic core. The system includes a spark gap which is
connected in series with a first capacitor. The series-connected
first capacitor and spark gap are connected across the ignition
coil secondary winding and a second capacitor is coupled to the
ignition coil primary winding and to a DC source of electrical
energy. Circuit means are provided for charging the second
capacitor and for discharging it through the primary winding in
timed relation to engine operation. This produces breakdown of the
spark gap in the secondary circuit and subsequent oscillations in
this circuit. The secondary circuit oscillations are at a frequency
f defined by the expression f = V.sub.m /4N.sub.s .PHI..sub.s where
V.sub.m is the instantaneous maximum voltage across the first
capacitor, N.sub.s is the number of turns in the secondary winding
of the ignition coil and .PHI..sub.s is the magnetic flux enclosed
by the secondary winding of the ignition coil at saturation of its
ferromagnetic core.
The present invention is an improvement over the capacitor
discharge ignition system described above in that it provides an
ignition system which operates in a ferroresonant mode as defined
by the above expression, but which also provides sustained and
controllable spark duration characterized by ferroresonant
oscillations in the secondary circuit of the ignition coil.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a capacitor discharge
ignition system which has controllable spark duration.
Another object of the invention is to provide an ignition system
which is characterized by sustained oscillation in the secondary
circuit of an ignition coil at ferroresonant frequency f = V.sub.m
/4N.sub.s .PHI..sub.s.
A further object of the invention is to provide an ignition system
that causes an alternating current to flow through the gap of a
spark plug.
A still further object of the invention is to provide an ignition
system which causes a spark discharge or breakdown in the gap of a
spark plug subsequent to which the spark is sustained and
ferroresonant oscillations occur in the secondary circuit of the
ignition coil for a predetermined time interval.
Still another object of the invention is to provide an ignition
system having restrike capability such that multiple sparks of
sustained duration may be produced within the gap of the spark plug
during one combustion cycle in a combustion chamber of an internal
combustion engine.
A capacitor discharge ignition system in accordance with the
invention comprises an ignition coil having first and second
primary windings, a secondary winding and a ferromagnetic core
about which the windings are wound. A spark plug has electrodes
spaced to form a spark gap. One of the electrodes is coupled to one
terminal of the secondary winding and the spark gap is connected in
series with the first capacitor. One terminal of the capacitor is
coupled to the other terminal of the secondary winding. A second
capacitor is coupled to the first primary winding and a DC source
of electrical energy is provided.
First circuit means are coupled to the second capacitor and to the
first primary winding. The first circuit means controls the
charging of the second capacitor from the DC source of electrical
energy and controls its discharge through the first primary winding
in timed relation to operation of the engine. Second circuit means,
coupled to the second primary winding, are provided for producing a
fixed frequency oscillatory current in the second primary winding
for a predetermined time interval subsequent to each discharge of
the second capacitor through the first primary winding. The
discharge of the second capacitor through the first primary winding
and the subsequent supply of the fixed frequency oscillatory
current to the second primary winding produces, for at least a
portion of the predetermined time interval, a voltage in the
secondary circuit of the ignition coil which oscillates at a fixed
frequency f defined by the expression f = V.sub.n /4N.sub.s
.PHI..sub.s where V.sub.m is the instantaneous maximum voltage
across the first capacitor, N.sub.s is the number of turns in the
secondary winding and .PHI..sub.s is the magnetic flux within the
secondary winding when the core of the ignition coil is
magnetically saturated.
The invention may be better understood by reference to the detailed
description which follows and to the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1a and 1b together form a complete schematic diagram of a
capacitor discharge ignition system in accordance with the
invention;
FIGS. 2 through 13 are reproductions of actual voltage and current
waveforms observed on an oscilloscope; these waveforms have the
same time base and illustrate the phase relationships of signals
which occur at various points in the circuit shown schematically in
FIGS. 1a and 1b.
DETAILED DESCRIPTION
With reference now to the drawings, wherein like numerals refer to
like parts in the several views, there is shown in FIGS. 1a and 1b
a complete schematic diagram of a capacitor discharge ignition
system capable of operation in a ferroresonant mode in accordance
with the invention. Various portions of the electrical circuit are
enclosed by broken lines and given designations with respect to
their function in the circuit. The complete ignition circuit of
FIGS. 1a and 1b is designated by the numeral 10.
In FIG. 1a, it may be seen that the ignition system 10 includes an
ignition coil 12 which has a first primary winding P1, a second
primary winding P2 and a secondary winding 5. The ignition coil 12
has a ferromagnetic core 14 which in the circuit 10 is capable of
being saturated repetitively after the initial breakdown of a spark
gap 26. More specifically, the secondary winding S of the ignition
coil has one of its leads connected to one terminal of a capacitor
C1. The other terminal of the capacitor C1 is connected to ground
at 16. A lead 18 extends from the other terminal of the secondary
winding S to the rotor 20 of a conventional distributor 22 for a
spark-ignition internal combustion engine. The distributor 22 has
eight contacts 24 which are repetitively and serially contacted by
the rotor 20 such that repetitive electrical contact is made with
the eight spark gaps 26 contained in the spark plugs of the
internal combustion engine. Thus, each of the spark plugs has one
of its electrodes, represented by a lead 25, connected to the
secondary winding S of the ignition coil and has its other
electrode 27 connected to ground at 28. It should be noted that the
ground connections 16 and 28 are common and, therefore, each of the
spark gaps 26 is connected, sequentially as the rotor 20 rotates,
in series with the capacitor C1. The capacitor C1 need not be
located as shown in FIG. 1, but rather may be connected in series
with the spark gap 26, for example, by its insertion in the lead
18, the lead 25 or the lead 27. If the capacitor C1 is inserted in
the leads 25 or 27, a separate capacitor is required for each spark
gap. Similarly, a separate secondary winding S may be provided for
each of the spark gaps 26 if desired. Separate secondary windings S
and capacitors C1 for each of the spark gaps 26 may be housed
within the spark plug, for example, as depicted in the spark plug
design of U.S. Pat. No. 3,267,325 issued Aug. 16, 1966 to J. F.
Why.
The first primary winding P1 of the ignition coil 12 has one of its
terminals connected to ground at 30 and has its other terminal 32
coupled, through a saturable, ferromagnetic core inductor L2 and a
lead 34, to a capacitor C2. The capacitor C2 is connected to a
junction 36 formed between a resistor R1 and the anode of a
semiconductor controlled rectifier (SCR) Q7. The cathode of the SCR
is connected to ground. The SCR has a gate or control electrode 38.
The current limiting resistor R1 is connected through another
saturable, ferromagnetic core inductor L1 to a +350 volt DC source
of electrical energy. This voltage, as well as the other Dc
voltages shown in FIG. 1, may be obtained from a 12 volt DC source
of electrical energy, such as the storage battery 44 conventional
in motor vehicles, through use of a DC to DC converter well known
to those skilled in the art.
An input matching circuit, a duration gate generator, a restrike
oscillator, an SCR driver and an SCR switch comprise circuit means
for charging the capacitor C2 from the DC source of electrical
energy and for discharging this capacitor through the first primary
winding P1 in timed relation to operation of the engine. The
charging and discharging of the capacitor C2 in timed relation to
the engine operation may be obtained in the conventional manner by
a cam 40 mechanically coupled to the distributor rotor 20, driven
by the engine, and used to intermittently open and close a set of
breaker points 42, one of which is connected to ground and the
other of which is connected at a junction 46. Because the DC source
of electrical energy 44 has its negative terminal corrected to
ground has has its positive terminal connected through a resistor
R2 to the junction 46, the junction 46 is at ground potential when
the breaker points 42 are closed and is at the +12 volt potential
of the storage battery 44 when the breaker points are open. The
voltage rise at the junction 46 which occurs each time the breaker
points open is supplied to an input matching circuit to cause the
production of a spark in one of the spark gaps 26.
As indicated above, the circuitry 10 includes an input matching
circuit. The function of this circuit is to couple the pulses
occurring at the junction 46 to a duration gate generator. The
duration gate generator produces a pulse output signal which has a
controllable duration and which is supplied to the restrike
oscillator. The function of the restrike oscillator is to produce
one or more pulse signals during the duration of the signal from
the duration gate generator. Each pulse produced at the output of
the restrike oscillator is used to initiate the discharge of the
capacitor C2 through the ignition coil first primary winding P1.
The output pulses from the restrike oscillator circuit are supplied
to an SCR driver circuit which utilizes the restrike oscillator
pulses to produce pulse spikes which are applied to the gate 38 of
the SCR Q7. An interlock circuit is provided to prevent, when the
ignition circuit 10 is first put into operation, the supply of a
pulse to the gate electrode 38 until the capacitor C2 has had
sufficient time to charge. In the paragraphs which follow, the
above circuit portions are described in detail.
The input matching circuit includes a choke inductor L3 which has
one of its terminals connected to the junction 46 and which has its
other terminal connected to the cathode of a zener diode D1. The
anode of this zener diode is coupled to ground through a resistor
R3 connected in parallel with a noise suppression capacitor C3. The
anode of the zener diode also is connected through the series
combination of a DC blocking capacitor C4 and a current limiting R5
to the base of an NPN transistor Q1. The junction formed between
the capacitor C4 and the resistor R5 is connected to the cathode of
a zener diode D2 whose anode is connected to ground. A resistor R4
is connected in parallel with the zener diode D2. The emitter of
the transistor Q1 also is connected to ground and its collector is
connected through resistors R6 and R7 to a +18 volt DC supply lead
48.
The function of the resistor R3 and capacitor C3 is to suppress
high frequency noise signals that may appear at the anode of the
zener diode D1. The capacitor C4 permits the positive step voltage,
which occurs at the junction 46 when the breaker points 42 open, to
momentarily pass through the resistor R5 to the base of the
transistor Q1 to render it momentarily conductive in its
collector-emitter output circuit. This permits current to flow
through the resistors R7 and R6 to ground.
The duration gate generator has a blocking capacitor C5 connected
to the junction formed between the resistors R6 and R7. The
opposite terminal of the capacitor C5 is connected through a
current limiting resistor R9 to the base of a PNP transistor Q2.
The junction formed between the capacitor C5 and the resistor R9 is
connected through a resistor R8 to the voltage supply lead 48. The
emitter of the transistor Q2 also is connected to the supply lead
48 and its collector is connected through series-connected
resistors R10, R11 and R12 to a -18 volt DC supply lead 50. The
resistor R12 is variable and controls the duration (total length of
time) of multiple spark discharges produced in a given spark gap 26
during one combustion cycle in the engine. More specifically the
resistor R12 controls the duration of the output signal pulse from
the duration gate generator. In a reciprocating spark-ignition
internal combustion engine, the length or duration of this output
pulse is the length of time available for the production of one or
more sparks in the spark gap 26 in a given cylinder to cause
ignition of a combustible mixture of fuel and air and a resultant
power stroke of the piston in that cylinder.
The capacitor C6 has one of its terminals connected to the voltage
supply lead 48 and has its other terminal connected to the junction
formed between the resistors R10 and R11. Also connected to this
junction is the cathode of a clamping diode D9 which has its anode
connected to ground. The diode D9 limits the negative voltage at
this junction to one diode voltage drop below ground potential. The
junction formed between the resistors R10 and R11 also is connected
through a coupling capacitor C7 and a current limiting resistor R15
to the base of a PNP transistor Q3. The junction formed between the
capacitor C7 and resistor R15 is connected through a resistor R13
to the negative voltage supply lead 50. The collector of the
transistor Q3 also is connected through a resistor R15 to the
supply lead 50, and the emitter of this transistor is connected to
the positive voltage supply lead 48. The collector of the
transistor Q3 is connected through a resistor R16 to the base of an
NPN transistor Q4 whose emitter is connected to ground. A clamping
diode D3 has its cathode connected to the base of the transistor Q4
and has its anode connected to ground to limit the base voltage to
one diode voltage drop below ground potential. The output signal of
the duration gate generator is taken at the collector of the
transistor Q4 which is connected to pin 7 of a dual monostable
multivibrator U1, which as shown is a Teledyne type 342. A Texas
Instruments type 15342 or the equivalent also may be used for
U1.
The duration gate generator is a sawtooth generator which is
triggered when the transistor Q1 is rendered conductive, which
occurs, as previously stated, when the breaker points 42 open. When
the transistor Q1 is rendered conductive, the resistor R8 and
capacitor C5 differentiate the resulting negative voltage step at
the collector of Q1. The negative voltage spike which results is
applied to the base of the transistor Q2. This renders the
transistor Q2 conductive in its emitter-collector output circuit
for a time sufficient to permit the discharge of the capacitor C6
through the resistor R10 and the emitter-collector circuit of the
transistor Q2. The capacitor C6 will have previously been charged
to a voltage slightly in excess of 18 volts DC. The transistor Q3
is normally conductive in its emitter-collector output circuit due
to the flow of current from the voltage supply lead 48, through its
emitter-base junction, through the resistor R15, and primarily
through the resistor R13 to the negative voltage supply lead 50.
However, when the capacitor C6 discharges, a positive voltage
approximately equal to the voltage on the supply lead 48 appears at
the junction formed between resistors R10 and R11. This voltage is
applied through the capacitor C7 and the resistor R15 to the base
of the transistor Q3 to render it nonconductive. The transistor Q3
remains nonconductive for the length of time required for the
capacitor C6, after the transistor Q2 again becomes nonconductive,
to recharge through the series resistors R11 and R12. Typically,
the transistor Q3 is nonconductive for a time period of from 1 to 5
ms. When the transistor Q3 is rendered nonconductive and for so
long as it is nonconductive, the transistor Q4 has no base drive
and also is nonconductive which results in the application of a
positive voltage at the pin 7 of the dual monostable multivibrator
U1.
The dual monostable multivibrator U1 has one monostable
multivibrator with an input A.sub.1 and an output Q.sub.1. The
other monostable multivibrator in the integrated circuit U1 has an
input A.sub.2 and an output Q.sub.2. By the connection of the
Q.sub.1 output to the A.sub.2 input and the connection of the
Q.sub.2 output to the A.sub.1 input, as is accomplished by the
connection of the lead 52 between the pins 5 and 10 and the
connection of the pins 6 and 11 at a junction 54, the dual
monostable multivibrator U1 becomes a pulse generator, the output
of which is taken at its pin 2. The Q.sub.1 output at pin 2
alternates between a high voltage level of about 10 volts and a low
voltage level near ground potential. With the circuit values
indicated in the drawings, the high voltage portion of the signal
at pin 2 is approximately 68 percent of the signal period. Dual
variable resitors R18 and R19 are connected, respectively, through
a resistor R20 and a capacitor C9 to the pins 3 and 4 and through a
resistor R21 and a capacitor C10 to the pins 12 and 13. These
components determine the duty cycle or pulse width at output pin 2
of the multivibrator and permit the period of the signal at pin 2
to be varied from about 0.30 ms to 1.5 ms. The period of the signal
at pin 2 represents the restrike delay, that is, the delay between
multiple ignition sparks produced in each of the spark gaps 26 by
repetitive triggering of the SCR Q7.
The dual monostable multivibrator U1 is triggered or gated when the
output circuit of the transistor Q4 is rendered nonconductive. When
the transistor Q4 is conductive, the signal at pin 2 of the dual
monostable multivibrator U1 remains constant at a low voltage
level, but when the transistor Q4 becomes nonconductive, gating
multivibrator U1, the signal at pin 2 becomes a series of pulses
which continually gate the SCR Q7 to produce a spark in a spark gap
26 each time a pulse occurs at pin 2. These repetitive and
restriking sparks continue to occur until the transistor Q4 is once
again rendered conductive.
The dual monostable multivibrator U1 receives its positive voltage
supply from a voltage regulator comprising a resistor R17 connected
in series with the parallel combination of a zener diode D4 and a
capacitor C8. The junction formed between these components is
connected to the voltage supply pin 16 of U1 and also is connected
to the variable resistors R18 and R19. Pin 8 of the multivibrator
U1 is connected to ground. Pin 2 of the multivibrator is connected
through a current limiting resistor R22 and a zener diode D5 to the
base of an NPN transistor Q5.
The transistor Q5 is located in the SCR driver portion of the
circuit 10 and has its emitter connected to ground. Its collector
is connected through a resistor R27 to the voltage supply lead 48
and also is connected through a current limiting resistor R28 to
the base of PNP transistor Q6. The emitter of the transistor Q6 is
connected to the voltage supply lead 48 and its collector is
connected through a resistor R29 and a lead 60 to a -18 volt DC
voltage supply. The collector of the transistor Q6 also is
connected, through a series circuit including differentiating
capacitor C12, resistor R30 and zener diode D8, to the gate
electrode 38 of the SCR Q7.
The waveforms shown in FIGS. 2 through 13 are representations of
signals which occur at various points in the circuit schematically
illustrated in FIG. 1, with the exception that the waveforms 11, 12
and 13 pertain to a 35 mil spark gap located in air at atmospheric
pressure rather than to a spark gap located in the cylinder of an
operating internal combustion engine.
FIG. 2 shows the voltage waveform that occurs at pin 2 of the dual
monostable multivibrator U1. This voltage is the oscillatory output
voltage of the multivibrator which occurs so long as the input
transistor Q4 connected to its pin 7 is in a nonconductive state.
Of course, Q4 is rendered nonconductive each time, and for a
predetermined time established by the duration gate generator, that
the cam 40 opens the breaker points 42. On each positive going edge
of the pulses in FIG. 2, the transistor Q5 is rendered conductive.
This reduces its collector voltage to substantially ground
potential to cause the conduction of the PNP transistor Q6. When
nonconductive, the collector of the transistor Q6 is at
approximately -18 volts DC, but when rendered conductive, its
collector achieves a voltage of almost +18 volts DC. This step
voltage on the collector of the transistor Q6 is differentiated by
the capacitor C12 to produce a voltage spike which gates the SCR
Q7. The voltage spikes are represented in FIG. 6, which illustrates
the voltage spikes occurring on the resistor R30 at points
corresponding to the positive going edges of the pulses of FIG. 2,
which pulses occur at pin 2 of the multivibrator. Thus, it is
apparent that the SCR Q7 is gated or triggered on each positive
going edge of the oscillatory signal occurring at pin 2 of the
multivibrator U1 and that this continues so long as the transistor
Q4 is nonconductive. If the duration gate generator is adjusted
such that the transistor Q4 is nonconductive for 5 milliseconds and
if the restrike delay resistor R18 and R19 are adjusted such that
the signal of FIG. 2 has a period of 0.33 ms, then the gate 38 of
the SCR Q7 will receive 16 trigger pulses during the course of the
5 ms that the transistor Q4 is nonconductive. This produces a
corresponding 16 spark discharge in a single one of the spark gaps
26. It should be noted that 5 ms is approximately the time required
for the piston in an eight-cylinder, four-cycle reciprocating
internal combustion engine to travel from its top-dead-center
positin to its bottom-dead-center position when the engine is
operating at 6,000 rpm.
With respect to the interlock portion of the circuitry 10, it may
be seen that this circuit portion comprises NPN transistors Q8 and
Q9. The emitters of these transitors are connected to ground
potential. The collector of the transistor Q9 is connected, through
a diode D6, to the junction formed between the resistor R22 and the
zener diode D5. The collector of this transistor also is connected
through a resistor 23 to a lead 57 connected to a +18 volt DC
source of electrical energy. A current limiting resistor R25 is
connected between the lead 57 and the collector of the transistor
Q8. The collector of the transistor Q8 also is connected through a
current limiting resistor R25 to the base of the transistor Q9. A
series-connected resistor R26 and capacitor C11 are connected
between the lead 57 and ground potential. The junction formed
between the resistor R26 and the capacitor C11 is connected through
a zener diode D7 to the base of the transistor Q8. Upon the initial
application of the DC supply potential to the lead 57, the
transistor Q9 immediately is conductive in its collector-emitter
output circuit. This has the effect of connecting connecting the
pin 2 output of the multivibrator U1 to ground potential to prevent
the conduction of the transistor Q5 and, consequently, to prevent
the supply of a triggering Q5 and, consequently, to prevent the
supply of a triggering pulse to the gate electrode 38 of the SCR
Q7. At this time, the transistor Q8 is nonconductive in its output
circuit because the capacitor C11 forms an effective short circuit
of its base-emitter circuit. However, the continued application of
the DC voltage on the lead 57 causes the capacitor C11 to be
charged through the resistor R26.
When the voltage on the upper terminal of the capacitor C11 exceeds
the sum of the breakdown voltage of the zener diode D7 and the
base-emitter voltage drop required to render the transistor Q8
conductive, then the collector-emitter circuit of transistor Q8
becomes conductive and shunts the base-emitter circuit of the
transistor Q9. The transistor Q9 then becomes nonconductive and the
positive going edges of the oscillatory signal at pin 2 of the
multivibrator U1 are permitted to cause the repetitive triggering
of the gate electrode 38 of the SCR Q7. The time required to charge
the capacitor C11 exceeds considerably the time required to charge
the capacitor C2 connected to the first primary winding P1 of the
ignition coil 12. The capacitor C2 must be fully charged before the
SCR Q7 is triggered because the latter is self-commutated as a
result of the discharge of the capacitor C2 through it and the
first primary winding P1. Of course, the interlock circuitry shown
in FIG. 1a may be replaced by gate circuitry which prevents the
application of a trigger signal on the gate electrode 38 of the SCR
prior to the required charge level on the capacitor C2 being
attained.
When the SCR Q7 is nonconductive between its anode and cathode, the
capacitor C2 is charged from the +350 volt DC power suply through
the current path including the inductor L1, the resistor R1, the
inductor L2, the first primary winding P1 of the ignition coil 12
and the ground circuit. When the SCR Q7 is triggered by a positive
pulse applied to its gate electrode 38, a current spike is
produced. Two such current spikes, caused by two successive trigger
pulses applied to the gate electrode 38 are shown in waveform of
FIG. 9. It may be seen that these current spikes have an
alternating current waveform. At the end of the spike, the SCR Q7
is self-commutated. This self-commutation is aided by the saturable
inductor L2 which offers little impedance to current flow due to
its saturable character.
FIG. 10 shows the voltage across the first primary winding P1 upon
the occurrence of the current spikes shown in FIG. 9. It may be
seen that this voltage is oscillatory, that it has a voltage spike
corresponds to the breakdown of one of the spark gaps 26, and that
the amplitude is substantially constant for the time interval
during which current flows through the spark gap (this current is
shown in FIG. 11 hereinafter described).
The sustain oscillator, the sustain gate, the sustain driver and
the sustain power amplifier generally comprise circuit means for
producing a fixed frequency oscillatory current in the second
primary winding P2 for a predetermined time interval subsequent to
each discharge of the capacitor C2 through the first primary
winding P1. The sustain gate is triggered by a signal which
triggers the SCR Q7 and produces oscillations of a square-wave
character and of fixed frequency. These oscillations receive
current and power amplification through the sustain driver and
sustain power amplifier circuits, and the amplified oscillatory
currents flow through the second primary winding P2 of the ignition
coil 12.
The sustain oscillator includes a dual monostable multivibrator
integrated circuit U2. The dual monostable multivibrator U2 as
shown has the pin connections of a Motorola Semiconductor
Corporation type MC 667, but equivalent devices may be substituted.
Dual monostable multivibrator U2 has its Q.sub.2 output connected
to its T.sub.1 input and has its Q.sub.1 output connected to its
T.sub.2 input. Thus, lead 64 interconnects pins 1 and 8 of U2 and
pins 6 and 13 are interconnected at a junction 66 which forms the
trigger input to the multivibrator U2. The trigger input is
supplied via a lead 68 connected to the collector of a transistor
Q11. The emitter of the transistor Q11 is connected to ground.
A lead 62 is connected to the junction 54 connected to pins 6 and
11 of the dual monostable multivibrator U1 in the restrike
oscillator. The signal on these pins is the same as the pin 2
signal shown in FIG. 2. Lead 62 is connected through a resistor R31
to the cathode of zener diode D10, the anode of which is connected
to the base of NPN transistor Q10. The emitter of the transistor
Q10 is connected to ground and its collector is connected through a
current limiting resistor R33 to a +18 volt DC source of electrical
energy. A resistor R32 is connected to this source and to the
junction formed between the resistor R31 and the cathode of the
zener diode D10. The collector of the transistor Q10 also is
connected through a current limiting resistor R34 to the base of an
NPN transistor Q11. When the voltage on the lead 62 is at its high
voltage level, the transistor Q10 is conductive in its output
circuit and its collector voltage is substantially at ground
potential. This renders the transistor Q11 nonconductive in its
output circuit and its collector is isolated from ground potential.
On the other hand, when the signal on the lead 62 is a low voltage,
the transistor Q10 is nonconductive, which causes the transistor
Q11 to be conductive in its collector-emitter output circuit and
results in the connection of the pins 6 and 13 of the dual
monostable multivibrator U2 to substantially ground potential.
The dual monostable multivibrator U2 is connected as a square-wave
oscillator which has a duty cycle and period determined by the
parallel-connected resistors R35 and R36 connected across pins 10
and 11 and the capacitor C13 connected between pins 9 and 11 and by
the parallel-conected resistors R37 and R38 connected across pins 3
and 4 and the capacitor C14 connected between the pins 3 and 5.
Resistors R36 and R37 are variable to provide an oscillator output
signal on the Q.sub.1 output at pin 2 of the multivibrator U2 which
has a frequency variable between 17 KHz and 35.7 KHz. The output on
the pin 2 of the dual monostable multivibrator U2 is a low level
voltage whenever the voltage on pin 2 of the dual monostable
multivibrator U1 is a low voltage, and the voltage on pin 2 of the
dual monostable multivibrator U2 is oscillatory between 12 volts
and ground potential whenever the voltage on pin 2 of the dual
monostable multivibrator U1 is at a high voltage level. The
oscillatory voltage at pin 2 of the multivibrator U2 is applied
through a current limiting resistor R40 to the base of an NPN
transistor Q12. The emitter of the transistor Q12 is connected to
ground and its collector is connected through a current limiting
resistor R41 to a lead 58 connected to a +18 volt DC source of
electrical energy. The voltage supply to the multivibrator U2 is
obtained from a resistor R39 connected to the lead 48 and to the
parallel combination of a filter capacitor C15 and a zener diode
D11 which are connected between the pin 14 of U2 and ground
potential. This provides a regulated supply voltage for
multivibrator U2. Pin 7 of the multivibrator U2 is connected to a
ground lead 70.
The output signal of the sustain oscillator is obtained on a lead
72 connected to the collector of the transistor Q12. This signal is
shown in FIG. 4 where it may be seen that the voltage oscillates
between about +18 volts DC and 0 volts DC. Because each of the high
voltage-level pulses at pin 2 of the multivibrator U1 results in a
trigger signal being applied to the gate 38 of the SCR Q7, and from
the waveform of FIG. 4, it is clear that an oscillatory signal is
produced on the lead 72 of the sustain oscillator each time the SCR
Q7 is triggered. This oscillatory signal has a duration
corresponding to the duration of the high-voltage-level pulses
shown in FIG. 2. These sustained oscillations on the lead 72 cause,
in a manner hereinafter described, current oscillations in the
second primary winding P2 of the ignition coil 12.
With particular reference now to FIG. 1b, there is shown the
sustain gate, the sustain driver and the sustain power amplifier,
the functions of which are to provide current and power
amplification of the oscillatory signals occuring on the lead 72
which is connected through a current limiting resistor R48 to the
base of PNP transistor Q15 in the sustain gate. The emitter of the
transistor Q15 is connected to a +18 volt DC supply lead 74 and its
collector is connected through a current limiting resistor R49 to a
-18 volt DC supply lead 76. The voltage on the collector of the
transistor Q5 in the SCR driver portion of the circuitry is shown
in FIG. 3 as the complement of the signal on pin 2 of the dual
monostable multivibrator U1 and is supplied via a lead 59 and
through a current limiting resistor R42 to the base of a PNP
transistor Q13. The emitter of this transistor is connected to the
voltage supply lead 74 and its collector through a resistor R43 to
the negative voltage supply lead 76. Its collector also is
connected through a current limiting resistor R45 to the base of a
PNP transistor Q14. The collector of Q14 is connected through a
current limiting resistor R46 to the negative voltage supply lead
76 and its emitter is connected to the voltage supply lead 74.
A diode gate is formed by diodes D12, D13, D14 and D15. The anodes
of the diodes D12 and D13 are connected together and, through a
resistor R44, are connected to the collector of the transistor Q13.
The cathode and anode junction formed between diodes D12 and D14 is
connected by a lead 78 to the collector of the transistor Q15 and
the cathodes of the diodes D14 and D15 are connected, through a
resistor R47, to the collector of the transistor Q14. The junction
formed between the cathode of the diode D13 and the anode of the
diode D15 is connected by a lead 80, which is the output of the
sustain gate, to one terminal of a resistor R50 the other terminal
of which is connected to ground. The lead 80 also is connected
through a resistor R51 to the base of an NPN transistor Q16 and
through a resistor R52 to the base of a PNP transistor Q17.
Transistors Q16 and Q17 form a push-pull amplifier and thus have
their emitters connected together and to ground potential. The
collector of the transistor Q16 is connected through a current
limiting resistor R53 to the voltage supply lead 74, and the
collector of the transistor Q17 is connected through a resistor R54
to the negative voltage supply lead 76. Also, the collector of the
transistor Q16 is connected to the base of a PNP transistor Q18
whose emitter is connected to the voltage supply lead 74 and whose
collector is connected via a lead 82 and a resistor R55 to ground.
Similarly, the collector of the transistor Q17 is connected to the
base of NPN transistor Q19 whose emitter is connected to the
negative voltage supply lead 76 and whose collector is connected to
the lead 82 and, through the resistor R55 to ground potential. It
may be appreciated that when the transistor Q16 is conductive in
its collector-emitter output circuit, the transistor Q18 also is
conductive to permit current flow from the voltage supply lead 74
to the lead 82, and, through the resistor R55, to ground. Likewise,
when the transistor Q17 is conductive in its emitter-collector
output circuit, the output circuit of the transistor Q19 is
conductive to permit current to flow from ground, through the
resistor R55 and through the colector-emitter output circuit of the
transistor Q19 to the negative voltage supply lead 76.
As may be seen from FIGS. 3 and 4, prior to the occurrence of
oscillations on the lead 72, the voltage on this lead is at about
+18 volts, as is the voltage on the gate signal lead 59. Thus, the
emitter-base junctions of the transistors Q15 and Q13 are
reverse-biased and these transistors are non-conductive. In such
case, the voltage on the sustain-gate output lead 80 is at ground
potential. When the voltage at pin 2 of the dual monostable
multivibrator U1 rises to about 10 volts to cause the application
of a trigger signal on the gate lead 38 of the SCR Q7, the gate
signal on lead 59 falls to a few volts as shown in FIG. 3. At the
same time, the voltage on the lead 72, connected to the collector
of the transistor Q12 in the sustain oscillator, oscillates between
about +18 volts DC and substantially ground potential as shown in
FIG. 4. The low voltage on the lead 59 renders the transistor Q13
conductive. This results in the application of about +18 volts to
the base of the transistor Q14 and it is rendered nonconductive in
its output circuit. The oscillations on the lead 72 are applied
through the resistor R48 to the base of the transistor Q15 to
render its emitter-collector output circuit conductive and
nonconductive in a corresponding oscillatory manner. Thus, the lead
78 alternates between +18 volts and -18 volts. When the lead 78 is
at +18 volts, current flows from the collector of the transistor
Q13 through the resistor R44, through the diode D13 and into the
lead 80. At the junction formed between lead 80 and the resistor
R50 the current divides, part of it flowing to ground through the
resistor R50 and the remainder flowing through the resistor R51 and
base-emitter junction of the transistor Q16 to ground. When the
lead 80 is at -18 volts, currents flow from ground through the
resistor R50 and from ground through the emitter-base junction of
the transistor Q17 and the resistor R52 to the lead 80 where there
currents are combined. The combined current flows from the lead 80,
through the diode D15, the resistor R47 and the resistor R46 to the
negative voltage supply lead 76. Under such circumstances, the
voltage waveform on the lead 80 is as shown in FIG. 5.
The transistors Q16 and Q17 are alternately conductive during the
oscillatory voltage which occurs on the lead 72. These transistors
amplify the alternating voltage signal on the lead 80.
When the transistor Q16 is conductive on alternative half cycles,
the transistor Q18 also is conductive to provide current and power
amplifications. Similarly, when the transistor Q17 is conductive,
the transistor Q19 is also conductive to provide amplification. The
voltage on the collectors of the transistors Q18 and Q19, during
the oscillations on the lead 72, also oscillates between about +18
and -18 volts. This alternating voltage, when positive, is applied
through a current limiting resistor R56 to the base of a transistor
Q20 to render it conductive, and, when negative, is applied through
a current limiting resistor R56 to the base of a transistor Q21 to
render it conductive. The emitters of the transistor Q20 and Q21
are connected together and to ground, the collector of the
transistor Q20 is connected through a resistor R58 to the voltage
supply lead 74, and the collector of the transistor Q21 is
connected through a resistor R59 to the voltage supply lead 76. The
transistor Q20 and Q21 form a push-pull amplifier.
The collector of the transistor Q20 is connected through a current
limiting resistor R60 to the base of a transistor Q22, the emitter
of which is connected through a resistor R62 to the voltage supply
lead 74. The colector of the transistor Q21 is connected through a
current limiting resistor R61 to the base of a transistor Q23 whose
emitter is connected through a resistor R63 to the voltage supply
lead 76. The collectors of the transistors Q22 and Q23 are
connected together. A diode D16 has its cathode connected to the
emitter of the transistor Q22 and has its anode connected to the
collector of this transistor. Similarly, a diode D17 has its
cathode connected to the collector of the transistor Q23 and has
its anode connected to the emitter of this transistor. Transistor
Q22 is conductive when transistor Q20 is conductive, and transistor
Q23 is conductive when transistor Q21 is conductive.
The junction formed between the collectors of the transistors Q22
and Q23 is connected by a lead 84 to the junction formed between a
resistor R64 and a saturable inductor L4. The opposite terminal of
the resistor R64 is connected to ground. Lead 19 connects the
opposite terminal of the saturable inductor L4 to the second
primary winding P2 of the ignition coil 12 and the lead 21,
connected to the opposite terminal of this second primary winding,
is connected to ground. Thus, the resistor R64 is connected in
parallel with the series-connected saturable inductor L4 and second
primary winding P2. The alternating conduction of the transistors
Q22 and Q23 in response to the oscillations on the lead 72 causes
an alternating current to flow through the saturable inductor L4
and the second primary winding P2 of the ignition coil to sustain a
spark in the gap 26 of a spark plug for a time period determined by
the length of time the oscillation continues on the lead 72. The
alternating voltage across and current flow through the second
primary winding P2 are shown, respectively, in FIGS. 7 and 8.
As was previously mentioned, FIG. 9 shows the current flow through
the primary winding P1 for two spark discharges through a spark gap
26. It may be seen that two alternating current spikes occur, one
for each of the SCR Q7 gate signal pulses which occur as shown in
FIG. 6. These gate signal pulses result in conduction of the SCR Q7
and the discharge of the capacitor C2 through the first primary
winding P1. This breaks down a spark gap 26, causes ferroresonant
oscillations to occur in the secondary circuit of the ignition coil
12, and causes the sustain gate, sustain oscillator, and sustain
amplifier circuitry to produce alternating current in the second
primary winding P2. The frequency of this alternating current is
selected to sustain a ferroresonant mode of oscillation in the
ignition coil secondary circuit.
FIG. 11 depicts the current through a 35 mil spark gap, located in
air at atmospheric pressure, for two spark discharges, each of
which is initiated by the discharge of the capacitor C2 through the
first primary winding P1 and each of which is sustained for a
predetermined time interval as a result of the alternating current
flow through the second primary winding P2. It may be seen that
this current flow through the spark gap is alternating in
direction, that the initial amplitude and frequency, that is, for
about the first 75 microseconds of the spark discharge, is higher
than the fixed frequency and amplitude of current flow which occurs
thereafter, and that the alternating current flow through the spark
gap is nonsinusoidal, which is the result of ferroresonent
oscillation in the secondary circuit of the ignition coil 12, this
ferroresonent oscillation resulting from repetitive variation of
the ignition coil ferromagnetic core between saturated and
unsaturated conditions.
FIG. 12 shows the voltage across the 35 mil spark gap, located in
air at atmospheric pressure, during the current discharge through
this spark gap as depicted in FIG. 11. The waveform of FIG. 12 has
notch-like portions 86 which correspond to the current spikes shown
in FIG. 11, leading to strong arcs within the spark gap 26. The
spark is extinguished at the point 88. Following this, a sinusoidal
and decreasing amplitude oscillation 90 take place.
FIG. 13 depicts the voltage across the capacitor C1 for two spark
discharges corresponding to the current and voltage waveforms
shown, respectively, in FIGS. 11 and 12. It may be seen that the
frequency of this voltage across the capacitor C1 for about the
first 75 microseconds oscillates at a voltage and frequency which
is in excess of that which follows. The oscillations of voltage
across the capacitor C1 during this initial 75 microseconds is a
ferroresonant oscillation defined by the equation f = V.sub.m
/4N.sub.s .PHI..sub.s. The oscillations which follow also behave in
accordance with this equation, but the frequency of oscillation is
that produced by the alternating current flowing through the second
primary winding P2. In other words, the ferroresonant oscillations
lock-in at the fixed frequency of the sustaining alternating
current oscillations in the second primary winding P2. The voltage
V.sub.m across the capacitor C1 assumes a value defined by the
foregoing equation for operation at such fixed frequency.
The voltage and current waveforms shown in FIG. 2 through 13 were
obtained with an ignition coil 12 having a first and second primary
windings P1 and P2 each of one turn and a secondary winding of 160
turns. The primary windings P1 and P2 and the secondary winding S
were wound on a ferrite (manganese zinc) core having the shape of a
closed, hollow cylinder with a central core running along its axis.
The cylinder had an outside diameter of 42 millimeters and a height
of 29 millimeters. The primary and secondary windings were wound
about the central core. The capacitor C1 had a value of 500
picofarads. The remaining components in the circuit of FIGS. 1a and
1b were of the values indicated therein. The capacitance values are
given in microfarads, unless otherwise specified, and the
resistance values are in ohms or, as indicated, in kilohms.
The design of the saturable ferromagnetic ignition coil 12 is not
critical and may take various forms other than that described in
the preceding paragraph. Also, the value of the capacitor C1 is of
importance in producing ferroresonance in the secondary circuit
during the discharge of the capacitor C2 through the ignition coil
primary winding P1, but the capacitance C1 may be within a broad
range. Values in excess of 1,000 picofarads for the capacitor C1
have been used.
The DC voltage supply for charging the capacitor C2 and the value
of this capacitor must be sufficiently large to permit the
discharge of this capacitor through the first primary winding P1 of
the ignition coil 12 to produce a ferroresonant condition, as
depicted in FIGS. 7 through 13, in the ignition system.
The circuitry of FIGS. 1a and 1b is designed to provide multiple
sustained sparks during a given combustion cycle in a given
combustion chamber of an engine. If it is desired to produce only
one sustained spark per combustion cycle, then the circuitry may be
simplified considerably. Of course, a transistorized ignition
system using a pulse generator driven by a distributor or the like
may be used in place of the cam 40 and breaker points 42. Such
breakerless ignition systems are well known.
The inventors have found that the first and second primary windings
P1 and P2 may, if desired, be replaced by a single primary winding
connected to the SCR Q7 in the manner shown in FIG. 1a, but also
having its terminal leads connected, for example, by the leads 19
and 21 in FIG. 1b, to the output of the sustain oscillator.
* * * * *