U.S. Patent Aug.

7, 1979 Sheet 1 of 13 4,163,437

United States Patent (19) 11 4,163,437
Notaras et al. 45) Aug. 7, 1979
54 TRANSISTORIGNITION CIRCUIT 3,878,452 4/1975 Haubner et al. .. ... 123/148 E
3,878,824 4/1975 Haubner et al. .. ... 123/148 E
(75) Inventors: John A. Notaras; Angelo L. Notaras; 3,881,458 5/1975 Roozenbeek et al. ... 123/148 E
James P. Williams, all of Sydney, 3,938,491 2/1976 Mazza ................... ... 123/148 E
Australia 3,963,015 6/1976 Haubner et al. ................. 123/148 E
73 Assignee: Solo Industries Pty. Limited, New FOREIGN PATENT DOCUMENTS
South Wales, Australia 45-4924 2/1970 Japan ................................... 123/148 E
(21) Appl. No.: 732,370 Primary Examiner-Charles J. Myhre
22 Filed: Oct. 14, 1976 Assistant Examiner-Andrew M. Dolinar
30 Foreign Application Priority Data Attorney, Agent, or Firm-Henry M. Bissell
Oct. 23, 1975 AU Australia .............................. PC3692 57 ABSTRACT
Nov. 18, 1975 AU Australia ... ... PC4O13 The present invention discloses an ignition system for
Dec. 19, 1975 AU Australia ... ... PC4350 internal combustion engines. The ignition system is
Jan. 30, 1976 AU Australia ... . . PC4678 particularly applicable to such engines including a mag
Mar. 19, 1976 AU Australia ... ... PC5272 netO.
Jun. 11, 1976 AU Australia .............................. PC6234 The ignition system includes a semi-conductor ignition
51) Int. C.’................................................ FO2P1/08 circuit in which a first transistor has its collector-emitter
52 U.S. C. ......................... 123/148 E; 123/148 AC; conduction path connected in series with the primary
123/149 C; 123/149 D; 315/209 T; 31.5/218 winding of an ignition coil assembly. A resistor is con
58 Field of Search........... 123/148 E, 148 D, 148 R, nected between base and collector of the first transistor
123/148 AC, 149 R, 149 C, 149 D; 315/209 T, to permit it to conduct. A control circuit connected
218 between the base of the first transistor and the primary
56 References Cited winding, turns the first trnasistor off when it is desired
to interrupt the primary winding current.
U.S. PATENT DOCUMENTS
The ignition system also includes a magneto ignition
3,484,677 12/1969 Piteo ................................ 123/148 E coil assembly which has a low inductance primary
3,548,800 12/1970 Lombardini ... 23/148 E winding having a relatively low number of turns. The
3,559,134 1/1971 Daley ................................... 336/205 coil assemblies of the present invention are generally
3,822,686 7/1974 Gallo...... a so a 123/148 E unsuitable for use with conventional mechanical
3,831,570 8/1974 Compton et al. ................ 123/148 E
3,861,372 1/1975 Shibukawa et al. ............. 123/148 R breaker points.
3,864,621 2/1975 Haubner et al. ................. 315/209 T
3,864,622 2/1975 Haubner et al. ................. 133/148 E 22 Claims, 44 Drawing Figures
U.S. Patent Aug. 7, 1979 Sheet 2 of 13 4,163,437
U.S. Patent Aug. 7, 1979 Sheet 3 of 13 4,163,437
U.S. Patent Aug. 7, 1979 Sheet 4 of 13 4,163,437
U.S. Patent Aug. 7, 1979 Sheet 5 of 13 4,163,437
U.S. Patent Aug. 7, 1979 Sheet 6 of 13 4,163,437

Fig.5.
U.S. Patent Aug. 7, 1979 Sheet 7 of 13 4,163,437
U.S. Patent Aug. 7, 1979 Sheet 8 of 13 4,163,437
U.S. Patent Aug. 7, 1979 Sheet 9 of 13 4,163,437
U.S. Patent Aug. 7, 1979 Sheet 10 of 13 4,163,437

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U.S. Patent Aug. 7, 1979 Sheet 11 of 13 4,163,437

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U.S. Patent Aug. 7, 1979 Sheet 12 of 13 4,163,437

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U.S. Patent Aug. 7, 1979 Sheet 13 of 13 4,163,437

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current must flow through the points in order to over
TRANSISTOR GNITION CRCUIT come and burn away any oil, dust, dirt and/or fungal
growth on the points. This ensures good conduction for
The present invention relates to internal combustion the flow of primary winding current whilst the contact
engines and provides a complete ignition system for 5 points are closed. In order to meet these requirements
such engines. The ignition system includes both transis coils for magneto ignition systems produce a short-cir
tor ignition circuits and coil assemblies. The invention is cuit primary winding current in the vicinity of 2 to 3
particularly suitable for use with internal combustion Amps when the points of the system are closed. Such a
engines having a magneto but is not limited thereto. current is considered to be the optimum required for
Hitherto conventional magneto ignition system have 10 self-cleaning and yet even so the cleaning, replacement,
comprised a coil and a set of contact points. The coil is and retining of the contact points of conventional mag
typically wound on the centre leg of a 3-legged, E neto ignition systems constitutes the major source of
shaped core of one leg of a 2-legged U-shaped core maintenance that these systems require.
formed from a plurality of laminations. Alternatively In order to overcome the abovementioned problems
the single leg of an I-shaped core may be used. The coil 15 with contact points, in recent years there have been
itself normally comprises a primary winding would several attempts to provide solid state electronic cir
close to the centre leg of the core and a secondary cuits which function to replace the conventional
winding which is coaxial with and exterior of the pri breaker points system. Such an electronic system is that
mary winding. described in U.S. Pat. No. 3,878,452 (corresponding to
A magnetic source, which typically comprises a mag 20 Australian Patent Application No. 59,669/73) in the
net or magnets, is rotatable past the coil and core in name of Robert Bosch G.m.b.H and commercially
synchronism with the crankshaft of the internal com available as a Bosch electronic ignition type 525
bustion engine. The contact points are connected across 1/217/280/032. The abovementioned commercially
the primary winding of the coil and are operable by available Bosch electronic ignition is fitted to a Husq
means of a cam which moves in synchronism with the 25 varna brand chain saw, for example.
magnet carrying magneto rotor. One side of the contact Whilst electronic ignition systems such as the above
points is generally earthed and one side of the second described Bosch system overcome the abovementioned
ary winding is generally also earthed by means of the disadvantages of contact points, they are expensive
frame and cylinder block of the internal combustion because the circuitry they employ requires the use of
engine. The unearthed end of the secondary winding of 30 expensive high voltage breakdown electronic devices.
the coil is directly connected to the spark plug(s) of the In addition, and more importantly, such electronic igni
engine. tion systems have not been able to provide starting at
The movement of the magnets in the magneto rotor low engine revolutions and the abovementioned Bosch
past the core induces a voltage pulse in the primary electronic ignition type, when fitted to a Husqvarna
winding of the coil. The magnitude of the open-circuit 35 chain saw, results in starting only at 1,100 R.P.M. which
primary winding voltage pulse is substantially propor corresponds to a rotor speed of 955 surface feet per
tional to the surface speed of the magnets in the mag minute.
neto rotor. The magnitude of the open-circuit primary Whilst the starting speed in the vicinity of 1,000
voltage pulse is also dependent upon fixed quantities R.P.M. is adequate for small chain saws, such a high
such as the shape and quality of the laminations and the starting speed is not adequate for most two and four
size and strength of the magnets. . stroke engines, especially those having heavy, high
The closure of the points is timed to substantially inertia parts such as heavy flywheels, heavy lawn
coincide with, or precede, the generation of the voltage mover blades and discs, and other such heavy inertial
pulse within the primary winding of the coil. When the loads connected to the engine crankshaft.
contact points close, the primary winding of the coil is 45 Such engines require starting speeds in the vicinity of
substantially short-circuited and therefore a current 400 to 600 R.P.M. and, to date, such low starting speeds
flows in the primary winding. This flow of current have been unobtainable by the abovementioned known
created in the primary winding is interrupted when the electronic ignition systems. Therefore such electronic
points open, thereby inducing a change in the magnetic ignition systems have not found favour and the conven
flux linking both the primary and secondary winding of 50 tional ignition systems including breaker points have
the coil. In consequence a voltage is generated in the continued to be used.
secondary winding of the coil which, because of the The number of two and four stroke engine made
large number of turns on the secondary winding, is of worldwide which are fitted with magneto ignition sys
sufficient magnitude to cause a spark within the cylin tems including breaker points is in excess of twenty
der of the internal combustion engine. 55 million engines per year. The number of small four
The major limiting factor in such conventional mag stroke engines made in the U.S.A. alone exceeds fifteen
neto ignition systems has hitherto been the condition of million per annum and the overwhelming majority of
the points. It has been found in practice that if a large these engines are fitted with magneto ignition systems
current flows through the points, the points rapidly having breaker points. Therefore the economic conse
become pitted and burnt. This result is caused by arcing 60 quences in any alteration in ignition systems used by
across the points produced by the back emf of the pri such manufacturers are very significant.
mary winding and reflected secondary winding induc In addition, not only are known electronic ignition
tance and by the sudden interruption to the flow of systems (excluding capacitor discharge systems) and the
current in the primary winding. magnetos for such systems unsuitable for the bulk of
Furthermore internal combustion engines are often 65 such engines because they are incapable of producing
required to operate in dirty and dusty conditions and starting at speeds between 400 and 600 R.P.M., but in
therefore it is desirable that the contact points of the particular such known electronic systems are incapable
system be self-cleaning. For this to occur a sufficient of use where very low speed starting is required.
 4,163,437
3 4.
Very low speed starting is required in some applica FIG. 13 is a circuit diagram of a further embodiment
tions such as engines fitted with a decompression valve of the ignition circuit of the present invention incorpo
which reduces the compression resistance experienced rating automatic spark advance;
by the crankshaft during manual cranking of the engine. FIG. 14 is a graph of collector current Ic against time
Also very low speed starting is required in those engines 5 for the circuit of FIG. 13 at relatively low rotor speeds;
which are designed to be manually cranked by women FIG. 15 is a graph of collector voltage Vc against
and members of both sexes which are aged or infirm and speeds;time for the circuit of FIG. 13 at relatively low rotor
therefore do hot have sufficient physical strength to
create a high cranking speed. Such applications in 10 FIG. 16 is a graph of collector current Ic against time
which low starting speeds are especially advantageous speed; for the circuit of FIG. 13 at a relatively high rotor
are lawn mowers and motor cycles which are intended FIG. 17 is a graph of collector voltage Vc against
for use by members of all sexes and all ages.
It is the object of the present invention to provide an time for the circuit of FIG. 13 at a relatively high rotor
ignition system which does not require points and 5 speed; FIG. 18 is a circuit diagram of an embodiment of the
which enables reductions in engine starting speeds to be ignition circuit of the present invention incorporating a
achieved.
The present invention encompasses both ignition Lambda diode;
FIG. 19
circuits and coil assemblies. The ignition circuits of the of the present is a circuit diagram of another embodiment
present invention may be used with conventional coil 20 FIG. 20 is ainvention circuit
incorporating a Lambda diode;
diagram of a still further embodi
assemblies and improved results are obtained. In addi ment of the ignition circuit of the present invention;
tion the coil assemblies of the present invention may be FIG. 21 is a circuit diagram of a modification to any
used with conventional electronic ignition circuits and electronic ignition circuit which enables battery assist
improved results are also obtained. ance at starting and low speed starting to be provided;
However, when both the ignition circuits and coil 25 FIG. 22 is another embodiment of the circuit of FIG.
assemblies of the ignition system of the present inven 21;
tion are used together, not only are further improve FIG. 23 is a graph of collector current Ic against time
ments in results obtained, but advantages are achieved for the circuits of FIG. 21 and FIG.22;
which enable the total cost of the ignition system as a FIG. 24 is a circuit diagram of one embodiment of a
whole to be significantly reduced. 30 modified ignition circuit which enables an electrical
Some embodiments of the present invention will now load to be driven by the primary winding;
be described with reference to the drawings in which: FIG. 25 is a further embodiment of the circuit of
FIG. 1 is a composite circuit diagram taken from the FIG. 24;
abovementioned U.S. Pat. No. 3,878,452 which is FIG. 26 is a modification to the circuit illustrated in
known prior art; 35 FIG. 24 which enables a chain saw safety brake to be
FIG. 2 is a circuit diagram of a first embodiment of operated from the primary winding;
the ignition circuit of the present invention; FIG. 27 is a circuit diagram of an embodiment of the
FIG. 3 is a circuit diagram of the preferred second present invention in which the primary winding of the
embodiment of the ignition circuit of the present inven ignition coil is selectively tapped in accordance with
tion; 40 different engine revolutions;
FIG. 4 is a graph of the open circuit voltage of the FIG. 28 is a circuit diagram of a further modification
primary winding L1 of the ignition coil as a function of to the igntion circuit of the present invention which
time for two individual revolutions of the rotor R; enables adjustable speed control of the internal combus
FIG. 5 is a graph of the current Ip flowing in the tion engine to be achieved;
primary winding L1 as a function of time during two 45 FIG. 29 is a circuit diagram of another modification
individual revolutions of the rotor R for the circuit of of the ignition circuit of the present invention which
FIG. 3; prevents a maximum engine revolution rate being ex
FIG. 6 is a graph of the primary winding voltage Vp ceeded;
as a function of time under the conditions mentioned 50 FIG. 30 is a circuit diagram of yet another embodi
above in connection with FIG. 5; ment of the ignition circuit of the present invention
FIG. 7 is another graph of the primary winding cur which incorporates a Schmitt Trigger; and
FIG. 31 is a circuit diagram illustrating how the igni
rent Ip under the conditions specified above in FIG. 5 in tion circuit of the present invention is used for internal
the situation where multiple ignition takes place in a combustion engines having a battery rather than a mag
short period of time; 55 neto ignition system.
FIG. 8 is a circuit diagram showing the circuit of Referring now to FIG. 1, there is illustrated a circuit
FIG. 3 with temperature compensation; diagram which is a composite figure taken from U.S.
FIG.9 is a circuit diagram of a further embodiment of Pat. No. 3,878,452 assigned to Robert Bosch GmbH
the ignition circuit of the present invention; which represents an ignition system which is typical of
FIG. 10 is a circuit diagram similar to that of FIG. 9 60 those used hitherto in two respects. These are that a
illustrating still another embodiment of the ignition conventional ignition coil designed for operation of
circuit of the present invention; contact points is used, and secondly the semi-conductor
FIG. 11 is a circuit diagram of an embodiment of the device, which is used to substitute for the previously
present invention incorporating automatic spark ad used mechanical breaker points, is switched between
Vance; 65 non-conduction and saturation.
FIG. 12 is a circuit diagram of a still further embodi The ignition system itself comprises an ignition coil
ment of the present invention incorporating a diode having a primary winding L1 and a secondary winding
bridge; L2 which are magnetically coupled. A rotor R which
 4,163,437
5 6
carries one or more magnets is rotatable past the pri the circuit design consequences of this have been that
mary winding L1 so as to induce an approximately the semi-conductor devices are switched from non-con
sinusoidal voltage waveform therein for each revolu ducting to saturated conditions
tion of the rotor R. Accordingly the biassing circuits for the semi-con
As explained in more detail in the abovementioned ductor devices have been designed with a view to driv
U.S. Patent, induced voltages of negative polarity cause ing the semi-conductor switches into saturation. In con
a current to flow through the diode D4 and resistor R4 sequence the diodes D1 and D2 are provided connected
which returns to the primary winding L1. However, in series with the Darlington transistor TD of FIG. 1 to
positive polarity voltages induced in the primary wind ensure that the Darlington transistor TD becomes and
ing L1 cause sufficient current to flow through the 10 remains saturated. Whilst this circuit arrangement oper
resistor R1 and into the base of the Darlington transistor ates as intended by its designers, the cost of providing
TD, to allow the Darlington transistor TD to conduct the additional two diodes further increases the cost of
the primary winding current between its collector an the total circuit in addition to that described above in
emitter via the diode D1 and D2. The voltage drop relation to the power, and voltage ratings of the semi
produced across the diodes D1 and D2 when added to 15 conductor devices.
the collector saturation voltage of the Darlington tran In addition the gain of semi-conductor devices hav
sistor TD, ensure that there is sufficient voltage across ing high voltage ratings is generally low and this results
resistor R1 and the effective base-emitter junction of the in such devices being unable to produce low speed
Darlington transistor TD to cause sufficient base cur starting.
rent to flow through resistor R1 and into the base of the 20 FIG. 2 illustrates the circuit diagram of the first em
Darlington transistor TD. Accordingly transistor TD is bodiment of the ignition circuit of the present invention.
maintained in the saturated condition. The rotor R is as before and the magneto, or ignition
Resistors R2 and R3 together with diodes D3, D31 coil assembly, formed from primary winding L1 and
and DZ1 constitute a potential divider. The base of secondary winding L2 may be as before but is prefera
transistor T2 is connected to a point of intermediate 25 bly as will be described hereinafter. The remainder of
potential on the abovementioned potential divider and the circuit comprises a first transistor T1 having its
the collector-emitter conduction path of transistor T2 is collector-emitter conduction path connected in series
connected in parallel with the effective base-emitter with the primary winding L1. A resistor R1 is con
conduction path of the Darlington transistor TD. nected between collector and base of the transistor T1
As the positive voltage induced in the primary wind 30 and a transistor T2 has its collector-emitter conduction
ing L1 increases towards a predetermined voltage, the path connected across the base-emitter junction of the
voltage appearing across resistor R3 increases suffi transistor T1. The base of the transistor T2 is connected
ciently to allow the transistor T2 to be turned on. When to a point of intermediate potential on a resistive poten
this happens the base of the Darlington transistor TD is tial divider formed by resistors R5 and R6 which are
effectively connected to the emitter of the Darlington 35 connected in series across the primary winding L1.
transistor TD. Therefore the Darlington transistor TD As the rotor R rotates a quasi-sinusoidal voltage is
is switched off and the current flowing in the primary induced in the primary winding L1. In the circuit of
winding L1 is abruptly interrupted. This abrupt inter FIG. 2, during the time when the induced voltage in the
ruption of the primary winding current induces a high primary winding L1 is negative a relatively small cur
voltage in the secondary winding L2 in conventional rent flows through resistors R5 and R6 and no current
fashion. flows through transistor T1. However, when the in
The circuit of FIG. 1 suffers from several disadvan duced primary winding voltage is positive a small cur
tages the first of which is that a conventional mechani rent flows through resistor R1 and into the base of
cal breaker point type ignition coil assembly is used. As transistor T1. This base current allows the transistor T1
explained previously such conventional ignition coil 45 to conduct current induced in the primary winding L1
assemblies produce relatively high voltages and suffi but is not of a sufficient magnitude to permit the transis
cient current so as to enable the breaker points, for tor T1 to become saturated. Accordingly transistor T1
which they were designed, to carry sufficient current to conducts in its active region normally used when tran
be self cleaning. The maximum current produced by sistors are required to function as amplifiers rather than
such coil assemblies has always been below 3 or 4 Amps 50 switches. The voltage appearing at the collector of
to prevent excessive wear and burning of the breaker. transistor T1 is always greater than that required at the
points. However, the use of such a conventional coil base of the transistor T1 to bias the transistor in the
assembly means that the semi-conductor components of normal active region. The difference in voltage be
the ignition circuit must be able to withstand the high tween the base and collector of transistor T1 corre
voltages and powers produced by the ignition coil. In 55 sponds to the voltage drop produced in the resistor R1
consequence expensive semi-conductors having rela by the base current flowing through resistor R1.
tively high power and voltage ratings are required. As the voltage induced in the primary winding L1,
Such semi-conductors significantly increase the cost of indicated as Vp in FIG. 2, increases the voltage appear
electronic ignition circuits known hitherto. ing at the base of transistor T2 increases proportion
In addition, in the design of electronic circuits to 60 ately. Accordingly, after a predetermined period, the
replace conventional breaker points, the semi-conduc voltage at the base of T2 will have increased sufficiently
tor devices used have been considered as functional to not only permit transistor T2 to conduct between
equivalents of the mechanical breaker points. This is collector and emitter but also to drive transistor T2 into
quite understandable since the production of a high saturation. As a result the voltage appearing at the base
voltage in the secondary winding L2 is to be brought 65 of transistor T1 is only the collector-emitter saturation
about by the abrupt interruption to the current flowing voltage of the transistor T2 and this voltage is insuffi
in the primary winding L1, and this abrupt interruption cient to enable the transistor T1 to conduct. Therefore
is normally achieved by means of a switch. However, transistor T1 turns off and abruptly interrupts the cur
 4,163,437
7 8
rent flowing in the primary winding Li. The abrupt Ip to flow once again as illustrated in FIG. 5. The mag
interruption of the current flowing in the primary wind nitude that the primary winding current Ip would have
ing L1 induces a high voltage in the secondary winding attained at the particular rotor speed concerned is indi
L2 in known fashion to create the desired spark. cated by the dash and dot line in FIG. 5.
It will be seen that the circuit of FIG. 2 is able to 5 FIG. 6 is a graph of the voltage Vp appearing across
operate with very many fewer components than that of the primary winding L1 for each of the single rotor
the prior art circuit of FIG. 1. In addition, when the revolutions described above in connection with FIG. 5.
magneto or ignition coil pair of the present invention is It will be seen that when a negative primary winding
used in connection with the circuit of FIG. 2, the volt current Ip is flowing the diode D5 effectively clips the
age, current and power ratings of the transistors T1 and O voltage Vp. The voltage curve (1) illustrates the voltage
T2 are relatively light and therefore low cost transistors Vp when the rotor speed is insufficient to cause trigger
may be used. This use of low cost semi-conductors ing of the ignition circuit. However, the voltage curve
together with the reduced number of components in a (2) illustrates the position at higher rotor speeds and the
circuit substantially reduces the cost of the overall igni increased magnitude of the voltage Vp increases sinu
tion circuit. 15 soidally until a critical voltage Vt is reached at which
FIG. 3 illustrates the circuit diagram of the preferred triggering of the ignition circuit takes place.
embodiment of the ignition circuit of the present inven Then as explained above the primary current Ip is
tion. The circuit illustrated in FIG. 3 is similar to that interrupted abruptly by the Darlington transistor TD
illustrated in FIG. 2 save that a Darlington transistor and this interruption of current induces a back e.m.f.
TD is used in place of the above-described first transis 20 voltage spike across the primary winding L1. This volt
tor T1, a diode D5 is connected in parallel with the age spike has a magnitude Vs which is referred to as the
collector-emitter conduction path of the Darlington switched voltage. A series of oscillations having only
transistor TD, but with reverse polarity, and a small positive pulses are normally produced during the time
capacitor C1 is preferably connected between base and immediately after the interruption of the primary cur
emitter of the transistor T2 to assist in turning that tran 25 rent and then the negative cycle of clipped voltage is
sistor on at the time of ignition. The need for capacitor resumed.
C1 to become charged before T2 turns on prevents FIG. 7 illustrates the primary current Ip waveform
spurious firing of the ignition circuit. which is produced when a plurality of triggerings of the
The operation of the circuit of FIG. 3 will now be ignition circuit take place within a single cycle. Under
described in more detail with reference to FIGS. 4 to 7. 30
In FIG. 4 a graph of the open circuit voltage induced in these circumstances the transistor T2 is initially turned
the primary winding L1 as a function of time for a single on to initially interrupt the primary current Ip and then
revolution of the rotor R is illustrated. Two curves (1) quickly turns off again. Accordingly the primary cur
and (2) are illustrated, the former being the voltage rent Ip commences to flow once again but has a magni
induced when the rotor R is travelling at a lower speed, 35 tude in excess of the triggering current It. Therefore the
and the latter when the rotor R is travelling at a higher transistor T2 turns on once more to interrupt the pri
speed. The open circuit voltage induced in the primary mary winding current p. This process is repeated until
winding L1 is substantially proportional to rotor speed finally when the primary current pre-commences once
and therefore the amplitude of the induced voltage again, its magnitude is then below the triggering current
increases with increasing rotor speed. magnitude It.
FIG. 5 shows a graph of the current Ip flowing in the FIG. 8 illustrates a circuit diagram of an embodiment
primary winding L1. During the time when the voltage similar to that illustrated in FIG. 3 save that up to three
Vp induced in the primary winding is negative, a nega thermistors, RT1, RT2 and RT3, may be provided in
tive current flows through diode D5. When the induced the circuit to provide temperature compensation in
voltage Vp is positive, a positive current flows through 45 order that the operating characteristics of the circuit
Darlington transistor TD. The curve (1) illustrates the remain substantially the same with changes in the oper
current flowing through the Darlington transistor TD ating temperature of the circuit. Such changes in the
when the rotor revolutions are insufficient to cause operating temperature may be brought about owing to
ignition. Under these circumstances the maximum posi changes in ambient temperature, for example because
tive amplitude of the current Ip does not exceed a pre 50 the internal combustion engine is used in either a hot or
determined trigger current It. a cold climate, or through changes in the temperature of
The curve (2) of FIG. 5 illustrates the primary cur the circuit brought about because of its proximity to a
rent Ip when rotor revolutions are sufficient to cause warm internal combustion engine, or even self-heating
the transistor T2 to be switched on. It will be seen that caused by flow of electrical current. Generally only one
when the primary current Ip exceeds the trigger magni 55 of the thermistors is required.
tude It, the transistor T2 is switched on thereby switch Any one or any combination of the three thermistors
ing off the Darlington transistor TD and abruptly inter may be used, however, thermistors RT1 and RT3 are
rupting the flow of primary current Ip. This interrup negative temperature coefficient thermistors whilst
tion causes an induced voltage in the secondary wind thermistor RT2 is a positive temperature coefficient
ing L2 in known fashion. Whilst the transistor T2 re 60 thermistor. The thermistors themselves may be con
mains on no current flows through the Darlington tran structed from one or more thermistors or a thermistor
sistor TD. and a separate conventional resistor so as to control the
However, the transistor T2 normally ceases to con resistance characteristic of the effective thermistor as
duct during the same positive cycle of induced primary desired. For example, a series resistor may be connected
winding voltage, and at this time the voltage appearing 65 with the thermistor RT3 and this gives slight advance
at the base of the Darlington transistor TD is able to rise ment of the time of ignition with increasing operating
sufficiently to cause the Darlington transistor TD to temperature of the circuit. The thermistors are indi
conduct thereby allowing the primary winding current cated as being connected in the circuit by means of
 4,163,437
9 10
dashed lines to indicate that they may be used as alterna ing the operating cycle of the internal combustion en
tives if desired. gine and this effectively advances the time of ignition by
Referring now to FIG. 9, an embodiment of the igni 1 or 2 mechanical degrees of the rotor rotation.
tion circuit of the present invention is illustrated therein The resistor R8 and Zener diode DZ2 draw current
which is similar to FIG. 2 save that a diode D5 has been 5 via resistor R1. Therefore less current is available via
added which functions as the diode D5 in FIG. 3, and a resistor R1 to provide the base current for Darlington
further diode D6 has been interposed between the resis transistor TD. As a result the Darlington transistor TD
tive potential divider formed by resistors R5 and R6 and does not conduct until later than normal during the
the base of transistor T2. The function of diode D6 is to positive voltage pulse.
alter the time at which the transistor T2 is turned on for O Because the conduction of Darlington transistor TD
given values of resistors R5 and R6 since the potential is delayed more current is available at the beginning of
divider must supply a sufficient voltage to forward bias the positive pulse to begin charging capacitor C1. Thus
the diode D6 before base current is supplied to the when the Darlington transistor TD is conducting only a
transistor T2. short time is required before capacitor C1 has become
A voltage suppressor DS such as a Zener diode, surge 15 charged to the point where transistor T2 turns on. Thus
suppressing selenium rectifier, or the like, may be con the time of ignition is advanced.
nected across the primary winding L1 as shown in FIG. FIG. 12 illustrates a circuit of a further embodiment
9. The voltage suppressor DS is illustrated in dashed . of the ignition circuit of the present invention in which
lines to indicate that it is not essential for the operation a diode bridge formed from diodes D8 to D11 rectifies
of the circuit. 20 the quasi-sinusoidal voltage and current waveforms
The effect of voltage suppressor DS is to prevent the induced in the primary winding L1 and applies them to
magnitude of the positive voltage pulses induced in the a first transistor T1. The first transistor T1 has a resistor
primary winding L1 exceeding a predetermined limit. R1 connected between its base and collector and a sec
This applies whether the induced voltage pulse is ond transistor T2 having its collector-emitter conduc
caused by movement of the rotor R or by the back emf 25 tion path connected in parallel with the base-emitter
produced when the primary winding current is inter conduction path of transistor T1. A capacitor C1 is
rupted by transistor T1. connected between base and emitter of transistor T2 as
Since the peak positive voltage applied between col before. Therefore a series of positive pulses are applied
lector and emitter of transistor T1 is reduced by voltage to the transistor T1 at a rate 2 or 3 times that previously
suppressor DS, the voltage rating of transistor T1 (or 30 applied.
Darlington transistor TD) may be reduced. The unrectified pulses produced by the primary coil
Transistors of relatively low voltage rating generally L1 are applied directly to a potential divider comprising
have relatively high current gains. Therefore if voltage resistors R5 and R6 and diode D7. The base of transistor
suppressor DS and a high gain transistor T1 are used, T2 is connected to a point of intermediate potential on
the transistor T1 will be turned off by transistor T2 as a 35 the potential divider via a diode D6. A diode D5 is
result of a smaller positive voltage pulse induced in the connected in the diodebridge so as to be in parallel with
primary winding L1 than previously. As a direct conse the collector-emitter conduction path of the first tran
quence lower speed starting can be achieved since the sistor T1 as before and protects the transistor T1 from
magnitude of the induced primary winding voltage any excessive negative voltages.
pulse decreases with decreasing rotor speed. In addition 40 The presence of diode D7 in the potential divider
to the reduction in starting speed, the transistors having means that only the positive pulses result in current
relatively low voltage ratings also have a lower cost. flow through resistors R5 and R6. Thus the base of
FIG. 10 illustrates a circuit similar to that of FIG. 9 transistor T2 only receives a voltage sufficient to cause
save that a Darlington transistor TD is used in place of base current to flow into the transistor T2 during the
transistor T1 and a further diode D7 is provided in the 45 positive pulses produced by primary winding L1. In this
potential divider. Again the diode D7 delays the time of regard the circuit of FIG. 12 operates in a manner simi
ignition for given values of resistors R5 and R6 since the lar to those circuits described above, however, during
diode D7 must also be forward biassed before base the negative pulses produced by the primary winding
current can be supplied to the transistor T2. In addition L1, although there is a positive pulse applied to the
the capacitor C1 is provided to assist in turning on the SO transistor T1 which conducts the negative pulses of
transistor T2 as in FIG 3. It is to be understood that primary winding current, this current is not interrupted
further series connected diodes may be provided in during the negative pulses, since transistor T2 is not
addition to diode D7 to further delay the time of igni turned on. Therefore the current flowing in the primary
tion and that Zener diodes may also be provided in this winding L1 is interrupted at the same rate with the
position of the potential divider. 55 circuit of FIG. 12 as it is in the circuits of the previously
FIG. 11 illustrates a further embodiment of the igni described Figures, thereby achieving correct timing.
tion circuit in which either a series connected capacitor The diodes D6 and D7 of FIG. 12 are preferments
C2 and resistor R7 are connected in parallel with the and may be removed if desired. The action of the poten
resistor R5 of the circuit of FIG. 3, or a series connected tial divider formed by resistors R5 and R6 is then as
resistor R8 and Zener diode DZ2 are connected be 60 described above in FIGS. 2 and 3.
tween base and emitter of the Darlington transistor TD. The circuit shown in FIG. 13 enables the time of
These circuit additions are indicated by dashed lines to ignition to be advanced once engine revolutions have
indicate that they are alternative connections. reached a predetermined magnitude. The circuit com
The function of resistor R7 and capacitor C2 is to prises resistors R1, R5 and R6 and transistor T2 and
allow the voltage appearing at the base of transistor T2 65 Darlington transistor TD as before which are con
to rise more quickly during the positive cycle of the nected to the magneto comprising coils L1 and L2 via a
voltage Vp appearing across the primary coil L1. Ac diode bridge formed from diodes D12 to D15. Diode
cordingly the transistor T2 turns on more quickly dur D5 is connected as before and one of diodes D12 or D15
 4,163,437
12
preferably has a variable resistor R9 connected in series transistor Ti and the base of transistor T3. The diode
therewith. D5 is connected across the primary winding L1 as be
The operation of the circuit of FIG. 13 may best be fore.
understood with reference to FIGS. 14 to 17 which During negative voltage pulses produced in the pri
show the voltage and current curves for the circuit of 5 mary winding L1, the diode D5 conducts and the re
FIG. 13 at three different speeds. FIG. 14 shows the mainder of the circuit remains inactive. However, dur
collector current Ic of the Darlington transistor TD at ing positive voltage pulses, as the magnitude of the
two speeds, the first curve (1) representing a rotor speed voltage increases, a small current flows through the
which is too low to produce ignition and the second resistor R1 and into the base of transistor T1 which
curve (2) representing the current produced when the O enables transistor T1 to begin to conduct. Accordingly
rotor speed is sufficient to cause ignition. In both cases a small current flows through transistor T1 through the
the negative current pulses of the primary winding Lambda diode LD1 and into the base of transistor T3.
current Ip are indicated by dashed lines and have been Thus both transistors T3 and T1 are able to conduct and
rectified to form the collector current Ic. The presence pass the primary winding current which is of increasing
of resistor R9 acts to reduce the magnitude of these 15 magnitude.
rectified negative pulses as will be explained hereinaf The Lambda diode LD1 senses the voltage across the
ter. resistor R10 and the collector-base junction of the tran
The positive pulse of the current Ip is transmitted sistor T3. As the magnitude of the primary winding
through the diode bridge and in the case of curve (2) has current continues to increase, a predetermined current
a magnitude sufficient to trigger the transistor T2 and 20 level is reached at which the total voltage drop across
thereby cause the Darlington transistor TD to cease the resistor R10 and the collector-base junction of the
conduction. transistor T3 is sufficient to prevent conduction of the
FIG. 15 shows the similar situation for the collector Lambda diode LD1.
voltage Vc which appears between emitter and collec Therefore the transistor T3 does not receive any base
tor of the Darlington transistor TD. Again the negative 25 current and is turned off. In consequence the primary
voltage pulses of the primary winding voltage Vp have winding current is suddenly interrupted thereby induc
been rectified and as illustrated in curve (2) the speed of ing a high voltage in the secondary winding L2 and
the rotor is sufficient to cause ignition. creating a spark in known fashion as desired. The
The position when the rotor revolutions have in above-described procedure is repeated for every posi
creased sufficiently to cause advancement of the spark 30 tive current pulse.
is illustrated in FIGS. 16 and 17. FIG. 16 illustrates the A still further embodiment of the ignition circuit of
current waveform for the collector current Ic, the first the present invention is illustrated in FIG. 19 in which
rectified pulse of which will have attained a magnitude transistors T1 and T2, resistor R1 and diode D5 are
sufficient to cause triggering of the transistor T2. Ac connected as before. However, a third transistor T3 has
cordingly the Darlington transistor TD first interrupts 35 its emitter connected to the emitter of transistor T2 and
the primary current p at a time during the first negative its collector connected to the collector of transistor T1
pulse of primary winding current. Therefore the time of via a resistor R12. The base of transistor T2 and the
ignition has been advanced. The rotor revolution rate at collector of transistor T3 are connected via a resistor
which the advancement of the time of ignition first R11. The base of the transistor T3 is connected to the
occurs may be adjusted by altering the magnitude of the 40 junction of Lambda diode LD2 and resistor R19.
resistor R9. The greater the value of this resistance the Again during negative pulses produced in the pri
more the attenuation of the rectified negative current mary winding L1, the diode D5 conducts and the re
pulses and the greater the speed required for the auto mainder of the circuit is inactive. However, during each
matic spark advance to first come into action. Once this positive pulse produced in the primary winding L1, as
minimum speed has been attained there will be an ad 45 the magnitude of the pulse increases a current flows
vancement of ignition time with increasing speed. Ad through the Lambda diode LD2 and resistor R19. The
vancements of the order of 10 to 35 mechanical rotor voltage drop across resistor R19 is thus applied to the
degrees may be achieved. The collector voltage Vc base of the transistor T3. Therefore transistor T3 con
waveform during automatic spark advance is illustrated ducts through resistor R12 and thereby maintains the
in FIG. 17. SO collector of transistor T3 at a relatively low voltage.
In the event that the magnitude of the negative pull This relatively low voltage is insufficient to cause
se(s) produced by the rotor is lower than the magnitude enough base current to flow through resistor R11 and
of the positive pulse, then it is possible to remove the into the base of transistor T2, to turn transistor T2 on.
resistor R9 from the circuit of FIG. 13 since the attenua Therefore transistor T2 does not conduct and sufficient
tion function that resistor R9 provides is automatically 55 base current flows through resistor R1 and into the base
provided by the magneto construction. However, if the of transistor T1 to enable transistor T1 to conduct. In
variable resistor R9 is removed it is then not possible to consequence the primary winding current is primarily
adjust the engine revolutions at which the automatic conducted through the transistor T1.
advance first occurs. However, when the positive voltage pulse induced in
FIG. 18 illustrates the circuit diagram of a further 60 the primary winding L1 exceeds a predetermined mag
embodiment of the ignition circuit of the present inven nitude, the Lambda diode LD2 ceases to conduct.
tion incorporating a Lambda diode LD1. The magneto Therefore transistor T3 does not receive any base cur
and rotor R are as before and the collector-emitter path rent and is thereby turned off. When transistor T3 turns
of the transistor T1 is connected in series with a small off the potential at the collector of transistor T3 rises
resistor R10 and the collector-emitter path of a further 65 and sufficient current flows through the series con
transistor T3. The resistor R1 is connected between nected resistors R11 and R12 and into the base of tran
base and collector of the transistor T1 as before and a sistor T2 to turn transistor T2 on. As a result the base of
Lambda diode LD1 is connected between the emitter of transistor T1 is effectively connected directly to the
 13
4,163,437
14
emitter of transistor T1. Therefore as before transistor shows the position when no battery current is applied,
T1 abruptly ceases to conduct and the current flowing the dashed negative portions of the curve representing
in the primary winding L1 is interrupted as before. the primary winding current carried by the diode D5.
FIG. 20 illustrates yet another embodiment of the However, when the battery current Ib is supplied the
ignition circuit of the present invention. The circuit curve is effectively moved upwards and ignition is
comprises a primary winding L1 of a magneto as before achieved with a positive pulse of smaller amplitude
having a secondary winding L2. A transistor T1 has its since only a small positive pulse is required to increase
collector-emitter conduction path connected in series the total collector current Ic to the level of current, It,
with a resistor R13 across the primary winding L1. A which is required to trigger the circuit.
resistor R1 is connected between base and collector of 10 As the level of battery current Ib supplied increases,
the transistor T1 as before. A transistor T4 is connected the starting RPM decreases, which makes the circuit of
with its base-emitter junction in parallel with resistor FIG. 22 ideal for outboard motors, lawn mowers and
R13 and its collector connected to the base of transistor other applications to which internal combustion engines
T1. Diode D5 is directly connected between collector are put. Since the battery current is only drawn during
and emitter of transistor T1 as before. 15 starting the battery B2 may be a dry cell since large
During operation of the rotor R, voltage pulses are battery ampere-hour capacities are not required. If re
induced in the primary winding L1 as before and the quired the battery may also be a rechargeable battery
negative pulses so induced are clipped by means of the such as an NiCd or lead-acid battery.
diode D5. However, during the positive pulses, suffi If the battery current in FIG. 21 is increased to the
cient current flows through resistor R1 to allow transis 20 point where it substantially equals the triggering cur
tor T1 to conduct via resistor R13. This situation con rent It, then it is possible to achieve ignition at zero
tinues until the current flowing in the primary winding revolutions provided that the piston is properly located
L1 reaches a predetermined value at which time the in the cylinder relative to top dead centre (TDC). This
voltage drop across resistor R13 is sufficient to turn proper location of the piston can be achieved by ensur
transistor T4 on. As a result the base of transistor T1 is 25 ing that the flywheel stops each time the engine is used
effectively connected to a potential less than that of its in a predetermined position. This may be achieved by
emitter. As a result no current flows into the base of magnetic attraction between a magnet on the flywheel
transistor T1 and it switches off. Accordingly the cur and a magnet on the crankcase. Alternatively the
rent flowing in the primary winding L1 is abruptly flywheel may be manually turned prior to ignition to
interrupted thereby inducing a spark in the secondary 30 locate the flywheel in the desired location. Fuel is in
winding L2 as desired. jected into the cylinder(s) prior to activating the first
FIG. 21 illustrates a modification to any of the cir spark. The injection of the fuel and the activation of the
cuits illustrated herein including known prior art cir first spark may be accomplished in that order by a man
cuits in which a battery is available to assist during ual, automatic mechanical, or electrical operation.
starting so that ignition may be achieved at extremely 35 Referring now to FIG. 24 and previous circuits, the
low rotor revolutions. As shown in FIG. 21 a battery current generated in the primary winding L1 which
B1 is connected in series with the primary winding L1, flowed in the negative direction was previously passed
the polarity of the battery B1 being such that the pulses through bypass diode D5 and not put to any use. The
of positive current produced by the primary, winding circuit of FIG. 24 illustrates how the ignition circuit 1
L1 are increased in magnitude by current from the may be isolated by diode D17 and allowed to operate on
battery B1. The result of this effective current increase the positive current pulses it requires whilst a diode D18
is that the rotor revolutions required to cause ignition allows the negative pulses produced in the primary
are substantially reduced and lower speed starting is winding L2 to be transferred and applied to an electrical
thereby achieved. The ignition circuit indicated gener load 2.
ally by the numeral 1 of FIG. 21 may be any one of the 45 Such a load 2 may constitute the charging of a battery
magneto transistor ignition circuits illustrated herein B3 used for any purpose. For example, the battery B3
including known prior art circuits. may be used to power a small guide light located at the
FIG. 22 illustrates an embodiment similar to that of end of a manually directed nozzle through which liquid
FIG. 21, component 1 being an ignition circuit. As is pumped from a spray pack misting machine carried
shown in FIG. 22 a battery B2 is connected in series 50 on the back of an operator and operated by the internal
with a switch S1, and the primary winding L1 is con combustion engine having the primary winding L1 in its
nected in series with a diode D16. The switch S1 is magneto. Other possible loads include, but are not re
operable so as to connect the battery to the ignition stricted to, a capacitor C3 connected in parallel with an
circuit 1 only during cranking of the engine and after incandescent lamp L which operates as a pilot light or
ignition the switch S1 returns to its normal position in 55 as the above-described guide lamp. The lamp L. may
which diode D16 is short-circuited. Therefore during also be operated without the capacitor C3. A heating
cranking current flows from the battery B1 to the igni element RH which may be used to heat the handles
tion circuit 1 and is available to increase the effective and/or carburettor of a chain saw or other engines
magnitude of the positive current pulse applied to the intended for use in cold climates is an alternative load.
ignition circuit 1. Diode D16 prevents current flowing. Referring now to FIG. 25, where the amount of
from the battery B2 through the primary winding L1. power required for the load 2 is beyond that able to be
The result of the effective current increase is that the produced by the negative current pulses induced in the
rotor revolutions required to cause ignition are substan primary winding L1 of FIG. 24, then a larger primary
tially reduced and lower speed starting is thereby winding L1 of FIG. 24 may be produced and some
achieved. 65 fraction of the total number of primary turns tapped to
The position is illustrated in FIG. 23 which shows the provide the necessary effective primary winding for the
graph of the collector current Ic (see the detailed circuit ignition circuit. However, the negative pulses of current
of FIG. 21) as a function of time. The curve labeled (1) produced by the entire coil are available for operating
 4, 163,437 16
15
the load 2. Zener diode DZ3 and resistor R14 are pre The speed sensitive switch S2 may be any type of
ferments and function to clip the negative voltage switch. For example, switch S2 may be a mechanical
pulses at high engine speed and thus protect the load 2. switch which may conveniently be mounted on the
It is to be understood that the diodes D17 and D18 rotor or, alternatively, may be an electrical switch, the
are merely representative of the possible isolating cir operation of which is dependent upon the magnitude of
cuits to separate the ignition circuit 1 from the load 2. the current or voltage produced by the primary wind
For example, the diode D17 could be reversed and ing L1.
placed in the other lead leading from the ignition coil The circuit arrangement illustrated in FIG. 28 pro
L1 to the ignition circuit. vides an adjustable constant R.P.M. control system
The circuit shown in FIG. 26 is a modification to the 10 which is powered by the negative pulses produced in
circuit shown in FIG. 24 which enables a chain saw the primary winding L1. Diodes D17 and D18 and
safety brake (or similar mechanical device) to be oper resistor R14 and Zener diode DZ3 all function as be
ated from the primary winding L1. The ignition circuit fore. A capacitor C4 is connected in parallel with the
1 and diodes D17 and D18 are as illustrated in FIG. 24 resistor R14 and Zener diode DZ3 so as to be charged
whilst the Zener diode DZ3 and resistor R14 are as 15 by the abovementioned negative current pulses. Ac
illustrated in FIG. 25 and function as before. cordingly capacitor C14 provides a filtering action and
The electrical load 2 of FIG. 26 comprises a solenoid enables a relatively steady D.C. voltage to be applied
coil SC connected in series with a silicon controlled across resistor R14 and Zener diode DZ3.
rectifier TR. A strain sensitive resistor R15 is connected 20
A Wheatstone bridge, comprising resistors R20 and
between the gate of the SCRTR and the solenoid coil R21 and potentiometers R22 and R23, is connected in
SC as illustrated. The strain sensitive resistor R15 is parallel with the capacitor C4. A differential amplifier
associated with the handle of a chain saw such that, A has its inputs connected to the Wheatstone bridge so
when the handle is grasped by the hand of the operator, as to amplify any out-of-balance voltage produced by
the strain applied to the resistor R15 increases its resis 25 the Wheatstone bridge. The power supply for the am
tance. Accordingly the magnitude of the resistor R15 plifier A is obtained from the capacitor C4 and the
prevents sufficient gate current flowing into the gate of output of the amplifier A is connected to the base of a
the SCRTR to cause it to conduct whilst the handle of transistor T5. The collector-emitter conduction path of
the chain saw is held by the operator. the transistor T5 is connected in series with a solenoid
However, should the hand of the operator slip from 30 coil SC across the capacitor C4.
the handle of the chain saw, the resistor R15 is no It will therefore be seen that any out-of-balance volt
longer strained and therefore its resistance rapidly de age produced by the Wheatstone bridge will be ampli
creases. This change in resistance permits a sufficient fied by the amplifier A and applied to the base of transis
gate current to flow into the SCR TR which then tor T5 so as to control the current conducted by the
switches on. As a result the solenoid coil SC receives 35 solenoid coil SC. When the solenoid coil SC is ener
current from the negative pulses produced in the pri gized this moves the armature AR to the left as seen in
mary winding L1. When the solenoid coil SC is ener FIG. 28 against the action of a spring 5. The armature
gized this operates an armature (not shown) which in AR is also connected to a lever 8 which controls the
turn permits the safety brake (not shown) of the chain throttle setting of the carburettor 7 of the internal com
saw to operate. It will be seen therefore, that should the bustion engine. A spring 6 is connected between the
hand of the operator slip from the handle of the chain carburettor 7 and lever 8 so as to move the lever 8
saw, the chain saw is immediately braked so as to re towards the carburettor 7.
duce the likelihood of any injury being sustained by the The desired constant speed at which the engine is
operator. If desired resistor R15 may be replaced by a required to run is set by adjusting the resistance of po
pressure sensitive device or used in conjunction there 45 tentiometer R22. For a given value of resistance of the
with. potentiometer R22 an out-of-balance voltage will be
In FIG. 27 a circuit arrangement is illustrated which produced on the Wheatstone bridge and this is voltage
enables an ignition circuit 1 having semi-conductor applied, via amplifier A, to the transistor T5. Accord
devices with relatively low power and voltage ratings ingly transistor T5 changes the amount of current flow
to be used with safety, especially on internal combus 50 ing in the solenoid coil SC so as to move the armature
tion engines designed to run at high revolutions. The AR, and hence lever 8, to alter the throttle setting of the
problem arises that since the magnitude of the voltage carburettor 7. As a result the speed of the engine
produced in the magneto is substantially proportional to changes as does the resistance value of potentiometer
the speed of the rotor, then at high engine revolutions, R23. Both these changes reduce the out-of-balance volt
high voltages may be produced which could damage 55 age produced by the Wheatstone bridge and accord
low cost semi-conductor devices. In order to overcome ingly a feedback loop is established.
this problem a tapped primary winding L1 is provided It will be seen that any change in the operating condi
together with a rotor speed sensitive switch S2. tions of the engine results in a change in engine speed
At low engine revolutions the switch S2 connects the which is sensed by the Wheatstone bridge. The above
ignition circuit 1 to the terminal A of the primary wind described circuit accordingly operates to change the
ing L1 so that a maximum of voltage and current is position of the lever 8 and the resistance of potentiome
available to secure ignition at low speeds. However, ter R23 so as to return the engine speed to the desired
when the speed of the internal combustion engine in preset speed.
creases, the speed sensitive switch S2 connects the igni FIG. 29 illustrates an embodiment of the present
tion circuit 1 to a tapped point B on the primary wind 65 invention which enables the ignition circuit to include a
ing L1. The current and voltage generated at the tapped governor which prevents the engine revolutions ex
point Bare significantly reduced below those generated ceeding a predetermined level. In the circuit of FIG. 29
at A and accordingly the ignition circuit is protected. the resistors R1, R5 and R6 and transistors T1 and T2
 4,163,437
17 18
function as before in relation to the positive voltage from transistor T1 and turning transistor T1 off more
pulses produced in the ignition coil L1. quickly.
As engine revolutions increase the magnitude of the It will be seen that a regenerative effect quickly takes
negative voltage pulse produced in the primary winding place in which the reducing current flowing between
L1 increases and at a predetermined negative voltage connector and emitter of transistor T1 acts to turn tran
pulse magnitude the Zener diode DZ4 will be over sistor T2 on more strongly, thereby further reducing
come to permit the capacitor C5 to be charged via the the current flowing between collector and emitter of
Zener diode DZ4 and diode D19. The resistor R24 transistor T1. As a result the turn off time of transistor
connected in parallel with the capacitor C5 discharges T1 is decreased and a more abrupt interruption to the
the capacitor C5 at a predetermined rate. As engine 10 primary winding current is achieved. Such an abrupt
revolutions continue to increase the capacitor C5 will interruption is desirable since it assists in inducing a high
progressively become more charged, notwithstanding voltage spark in the secondary winding of L2 of the
the action of resistor R24, until such time as the capaci magneto.
tor C5 is sufficiently charged to forward bias diodes As mentioned previously the ignition circuit of the
D20 and D21. As a result the potential appearing at the 15 present invention is not limited to use with internal
junction of resistors R5 and R6 and the base of transis combustion engines having a magneto, but rather may
tor T2 is lowered thereby preventing transistor T2 from also be used with internal combustion engines which
being turned on as the first step in causing ignition. have a battery ignition system such as that commonly
Once diodes D20 and D21 have been forward biassed used in automobiles. FIG. 31 illustrates an embodiment
the next positive pulse produced by the ignition coil L1 20 of the ignition circuit of the present invention when
will cause a current to flow through resistor R5, and used with internal combustion engines having a battery
diodes D20 and D21 to discharge the capacitor C5 ignition system.
partially. Accordingly one or more engine cycles will The circuit of FIG. 31 comprises the battery B4 of
be completed without any ignition taking place and the 25 the battery ignition system connected in series with the
primary winding L3 of a battery ignition coil assembly.
engine revolutions will decrease. The engine revolu The primary winding L3 is connected in series with a
tions will continue to decrease until the magnitude of switch, which in the preferred embodiment comprises a
the negative voltage pulse is insufficient to overcome switching Darlington transistor TDS. Finally the
Zener diode D24 and charge capacitor C5. Therefore switching Darlington transistor TDS is connected in
diodes D20 and D21 will no longer be forward biassed 30 series with the ignition circuit of the present invention
and ignition will recommence. to complete the primary winding current path via the
It will therefore be seen that the circuit of FIG. 29 battery B4.
prevents the engine revolutions exceeding a predeter The primary winding L3 has a secondary winding L4
mined revolution rate and this rate may be adjusted by magnetically coupled thereto in conventional fashion.
changing the resistance of resistor R24, and/or the ca 35 Series connected resistors R28 and R29 are connected
pacitance of capacitor C5, and/or by selecting Zener in series with a switch S3 across the battery B4. The
diode DZ4 to have a different reverse breakdown volt switch S3 closes in synchronism with engine revolu
age. tions and may be either a mechanical switch, a hall
FIG. 30 is a circuit diagram of a Schmidt Trigger effect device, a light sensitive switch, or some other
embodiment of the ignition circuit of the present inven switching device. The base of the switching Darlington
tion. It will be seen that a resistor R26 is connected transistor TDS is connected to the junction of resistors
between the emitter of transistor T1 and the primary R28 and R29. Resistors R28 and R29 are selected such
winding L1 whilst a resistor R27 is connected between that when switch S3 is closed the switching Darlington
the base of transistor T1 and the collector of transistor transistor TDS turns on and permits conduction of
T2. The emitter of transistor T2 is connected to the 45
emitter of transistor T1 as before.
primary winding current.
As switching Darlington transistor TDS turns on, the
During negative cycles of the voltage produced in Darlington transistor TD begins to conduct since suffi
the primary winding L1, diode D5 functions as before. cient base current flows through resistor R1 into the
However, during positive cycles of the induced primary base of Darlington transistor TD and then through
winding voltage, resistors R1 and R27 supply sufficient 50 switching Darlington transistor TDS and primary
base current to transistor T1 to permit transistor T1 to winding L3. Therefore Darlington transistor TD con
conduct. Therefore as transistor T1 conducts the in ducts without going into saturation and allows primary
creasing pulse of positive current, so the voltage across winding current to flow from the battery B4 through
resistor R26 progressively increases. When the voltage Darlington transistor TD, switching Darlington transis
at the junction of resistors R5 and R6 has increased 55 tor TDS and primary winding L3. Some of the primary
sufficiently above the voltage appearing across resistor winding currentis diverted to flow through resistors R5
R26, base current begins to flow into transistor T2 and R6 and therefore, as before, when the potential at
which begins to turn on. the base of the transistor T2 increases sufficiently, tran
As transistor T2 begins to turn on, the base. current sistor T2 turns on to turn Darlington transistor TD off.
flowing into the transistor T1 is now partially diverted When Darlington transistor TD turns off the primary
and flows through transistor T2. Accordingly transistor winding currentisinterrupted thereby producing a high
T1 begins to turn off and the amount of current flowing secondary induced voltage as desired. The timing of
between collector and emitter of transistor T1 is re switch S3 is such that when the Darlington transistor
duced. As this current reduces so the voltage across TD has interrupted the primary winding current, then
resistor R26 is also reduced thereby increasing the volt 65 switch S3 opens so as to disconnect the bias circuit
age applied between base and emitter of transistor T2. formed from resistors R28 and R29 for the switching
This increase in base-emitter voltage turns transistor T2 Darlington transistor TDS. Accordingly to the switch
on more strongly, thereby diverting more base current ing Darlington transistor TDS turns off.
 4,163,437
19 20
This cycle is then repeated for as switch S3 closes, FIG. 41 is a cross-sectional view similar to FIG. 40 of
switching Darlington transistor TDS turns on, Darling a spool of a second embodiment;
ton transistor TD conducts and then interrupts primary FIG. 42 is a graph of peak open-circuit primary volt
winding current and finally switch S3 re-opens so as to age vs rotor speed characteristic of an embodiment of
turn switching Darlington transistor TDS off. the magneto coil assembly of the present invention
If desired, a potentiometer or resistor could be con when compared with known magneto coil assemblies;
nected in parallel with switching Darlington transistor FIG. 43 is a graph of the peak short-circuit primary
TDS to allow a current less than the triggering current current vs rotor speed characteristic of the abovemen
to flow in the primary winding L3 before switch S3 tioned coil assemblies; and
closes. When switch S3 closes the primary winding 10 FIG. 44 is a graph showing the peak watts delivered
current quickly exceeds the trigger current thereby by the abovementioned coils to a 1.5 ohm resistive load
quickly causing ignition. In this way reliable ignition at as a function of rotor speed.
high engine revolutions may be obtained. The cross-sectional view of FIG. 32 shows a conven
The ignition circuits of the present invention have tional magneto coil assembly configuration comprising
been fabricated using thick film hybrid integrated tech 15 magneto coils 10 mounted on the centre leg 11 of a
niques which result in circuits of small physical size. 3-legged permeable core 12 which is normally formed
Preferably the thermistors illustrated in FIG. 8 are from a plurality of steel laminations. The core 12 has a
formed on the same substrate as that on which the tran centre limb 11 and outer legs 13 and 14, which are
sistor T1 or Darlington transistor TD is formed. In this interconnected by means of a cross member 15. The
way the thermistors act very quickly immediately there 20 centre limb 11, cross member 15 and any one of the
is any change in the substrate temperature. The above outer limbs 13 and 14 surround the magneto coils 10 on
three sides thereof.
mentioned construction of the ignition circuits of the The magneto coils 10 themselves comprise a primary
present invention enables the ignition circuit to be winding 16 normally having from 200 to 300 windings
moulded together with the magneto or ignition coil and 25 of relatively thick wire. The primary winding 16 is
in very close proximity thereto. normally rectangular or square in cross-section and its
It is also to be understood that the circuits described
above using NPN transistors may be modified to use, longer side extends along the centre limb 11. Coaxial
for example, PNP transistors with attendent changes in with and spaced from the primary winding 16, is a sec
polarity. ondary winding 17 which is also normally rectangular
Since all the circuits described above will operate
30 or square in cross-section. The diameter of the second
from conventional magneto coil assemblies, the above ary winding wire is very much less than that used in the
primary winding and typically has a diameter of only
description of the present invention has been directed to about 0.002 inches. In addition the secondary winding
the circuit details of the present invention. However, 17 generally contains of the order of 10,000 turns. The
the performance of the above-described circuits, when 35 primary winding 16 and secondary winding 17 are nor
operated from conventional magneto coil assemblies mally encased within a moulded body 18 which is nor
normally used for mechanical ignition breaker points, mally formed from epoxy resin, low density PVC or
may be improved when operated from the magneto coil any other like material.
assemblies of the present invention. FIG. 33 is a view similar to that of FIG. 32 but illus
The magneto coil assemblies of the present invention trates a magneto coil assembly in which conventional
will now be described in more detail with reference to magneto coils 10 are mounted on a 2-legged permeable
the drawings in which: core 19. Again the permeable core 19 is normally
FIG. 32 is a cross-sectional view of a conventional formed from a a plurality of steel laminations and com
magneto coil assembly having a 3-legged permeable prises an inner leg 20 upon which the magneto coils 10
core; 45 are mounted and an outer leg 21. The legs 20 and 21 are
FIG. 33 is a cross-sectional view of a conventional joined by a cross member 22. The magneto coils 10
magneto coil assembly having a 2-legged permeable comprise a primary winding 16, a secondary winding 17
core; and a moulded body 18 as before. As in FIG. 32, the
FIG. 34 is a cross-sectional view of a conventional permeable core 19 illustrated in FIG.33 only surrounds
magneto coil assembly having an I-shaped permeable 50 the magneto coils 10 on three sides thereof. The mag
core; neto coils 10 of FIGS. 32 and 33 are sometimes mounted
FIG. 35 is a cross-sectional view of a conventional on cross member 15 or 22 respectively rather than inner
magneto coil assembly having a 2-legged permeable legs 11 or 20.
core with encompassing core limbs; In FIG. 34 a further conventional magneto coil as
FIG. 36 is a cross-sectional view of the magneto coil 55 sembly is illustrated. However, the permeable core 9
assembly of a first embodiment of the present invention comprises a cross member 8 upon which the coils 10 are
suitable for either 1, 2 or 3-legged permeable cores; mounted and part-circular side members 7. The assen
FIG. 37 is a cross-sectional view of the magneto coil bly of FIG. 34 is intended for location at a fixed position
assembly of a second embodiment of the present inven within the interior of an annular rotor whilst the assem
tion also suitable for either 1, 2 or 3-legged permeable blies of FIGS. 32 and 33 are intended for location at a
cores; fixed position external to the rotor.
FIG. 38 is a circuit diagram showing the preferred FIG. 35 is again a cross-sectional view of a conven
interconnection of the primary windings illustrated in tional magneto coil assembly manufactured by Briggs &
FIG. 37; Stratton. The magneto coils 10 have a primary winding
FIG. 39 is a side elevation of an embodiment of a coil 65 16, secondary winding 17, and moulded body 18 as
carrying spool of the present invention; before and are mounted on an encompassing permeable
FIG. 40 is a cross-sectional view of the spool of FIG. core 23 which is again normally formed from a plurality
39 taken along the line AA of FIG. 39; of steel laminations.
 4,163,437
21 22
The encompassing permeable core 23 comprises first windings namely first and second primary windings 38
and second legs 24 and 25 respectively joined by a and 39 respectively between which is located a second
mounting limb 26 which carries the magneto coils 10. ary winding 40. The windings 38, 39 and 40 are each
The first leg 24 and second leg 25 are respectively ex carried on a spool 32 as before. The primary windings
tended to form L-shaped limbs 27 and 28 which substan 5 38 and 39 are preferably connected in parallel as illus
tially enclose the magneto coils 10. The extremities of trated in the circuit diagram of FIG. 38. However, if
the L-shaped limbs 27 and 28 abut either side of a thin desired, the first and second primary windings 38 and 39
shim 29 of non-magnetic material. It will be apparent may be connected in series.
from FIG. 35 that the permeable core 23 by virtue of In addition, a single winding (either primary or sec
mounting limb 26 and L-shaped limbs 27 and 28, sub O ondary) may be located within two or more spools. In
stantially encompasses the magneto coils 10 on four this way the distance between the discs 34 and 35 may
sides thereof. For this reason the configuration of the be reduced. Thus the voltage appearing between each
encompassing permeable core 23 is to be contrasted layer of the coil is reduced since the number of turns per
with the configuration of the permeable cores 9, 12 and layer has been reduced. This winding technique there
19. 15 fore reduces the insulation requirements of the winding.
In conventional magneto coil assembly practise it is If desired, a number of spools may be integrally formed.
also known, where space immediately adjacent the A side elevation of one of the spools 32 shown in
magneto rotor is limited, to locate one of the above FIG. 36 or 37 is illustrated in FIG. 39 which shows the
described magneto coil assemblies away from the imme strands 41 of the secondary winding and also shows the
diate vicinity of the rotor. In this case a first winding 20 edge of the grooved inner surface 42 of both discs 34
and associated permeable core is located adjacent to the and 35.
rotor. The first winding is directly connected across the The nature of the grooved inner surface 42 may be
primary winding of the magneto coil assembly. This better seen in FIG. 40 which is a cross-sectional view of
arrangement is also within the scope of the present the spool 32 of FIG. 39 taken along the line AA. In this
invention. 25 embodiment the grooved surface 42 has a plurality of
The cross-sectional view of FIG. 36 shows the mag radial grooves 43 substantially equally angularly spaced
neto coils 30 of a first embodiment of the present inven around the disc. The function of the grooves 43 is to
tion which may be mounted on either the 3-legged permit epoxy resin to be introduced into the strands 41
permeable core 12 of FIG. 32, or the 2-legged permea of the winding and between the strands 41 and the discs
ble core 19 of FIG. 33. The outer leg 13 of FIG. 36 is 30 of the spool 32. The grooves 43 allow epoxy resin or a
drawn with broken lines to indicate this alternative flowable insulating material to permeate into the inte
permeable core arrangement. The permeable core con rior of the winding in order not only to secure the
figuration of FIG. 34 may also be used. strands 41 of the winding but also to assist in the electri
The magneto coils 30 themselves comprise a primary cal insulation of the winding. Because the insulation
winding 31 mounted in a spool 32 and a secondary 35 requirements of the primary winding(s) are less severe,
winding 33 mounted in a similar spool 32. Both the the grooved surface 42 may be smooth for the spool 32
primary winding 31 and the secondary winding 33 have carrying the primary windings 31, 38 or 39.
substantially rectangular cross-sectional areas, how FIG. 41 shows a second embodiment of the grooved
ever, in both cases the shorter cross-sectional coil di inner surface 42 of the spool discs and is a view similar
mension extends along the centre limb 11. to FIG. 40. FIG. 41 illustrates a grooved inner surface
The spools 32 may be fabricated from any convenient 42 having substantially parallel grooves 44. The parallel
nonmagnetic material and are of generally toroidal grooves 44 are easier to construct than the radial
shape having upper and lower discs 34 and 35 respec grooves 43 of FIG. 40 since although the spools 32 are
tively spaced apart by a central channel portion36. The normally moulded from plastics material, a mould or die
channel portion 36 may have the same internal cross 45 has to be fabricated. In the fabrication of such a mould
section as the cross-section of the centre limb 11, as or die, it is easier to make a series of parallel ridges
illustrated, or have a circular interior for ease of manu which will ultimately produce the parallel grooves 44,
facture. rather than construct a series of radial ridges which will
The spacing between the upper disc 34 and lower ultimately produce the radial grooves 43. Use of the
disc 35 of the spool 32 carrying the primary winding 31 50 parallel grooves 44 does, however, require the presence
will normally exceed the corresponding spacing for the of a ridge 45 extending substantially perpendicularly to
spool 32 carrying the secondary, winding 33. Although the grooves 44 across the inner surface 42. The ridge 45
the spools 32 illustrated in FIG. 36 have substantially is required to prevent the strands 41 forming the coil
equal external diameters, the external diameters of the from lodging in the grooves 44 whilst the coil or wind
spools 32 carrying the primary winding 31 and second 55 ing is being wound.
ary winding 33 may be different if desired. The spools The channel portion 36 may have a rectangular exte
32 carrying both windings 31 and 32 are preferably rior cross-section as illustrated in FIG. 40 or a circular
encased within a moulded body 18 as are the conven exterior cross-section as illustrated in FIG. 41. The
tional coils of FIGS. 32 to 35. latter cross-section is preferred since it enables a con
In addition the spools 32 may be located on the cross 60 stant tension to be maintained on the wire whilst the coil
members 15, 22, or 8, rather than the centre limb 11, if is being wound.
desired. The advantages of the magneto coil assemblies de
FIG. 37 illustrates a second embodiment of the mag scribed in FIGS. 36 to 41 relate both to the performance
neto coil assembly of the present invention in a view and quality of the coils and also to the cost of their
similar to that of FIG. 36. The 3-legged permeable core 65 manufacture.
12 is illustrated for convenience but the 2-legged perme The spools 32 may be easily moulded from plastics
able core 19 or I-shaped core 9 could be used if pre material and the desired winding would therein. The
ferred. The magneto coils 37 of FIG. 37 comprise 3 winding and spool may then be stored ready for assem
 4,163,437
23 24
bly as required without the need for an outer coil to be magneto coil assembly of the present invention consid
wound around a former which already includes an inner erably improves the performance of the abovemen
coil. In addition the separate spool construction enables tioned Bosch electronic ignition circuit also.
additional insulation such as interleaved sheets of paper, Furthermore when the abovementioned magneto coil
polyester, or the like between layers of the high voltage assembly of the preferred embodiment of the present
secondary winding 17, to be removed without any re invention is used with the abovementioned circuit of
duction in the effective insulation performance of the FIG. 3 then a spark is first produced at 150 R.P.M.
coil. The ability to rely for insulation solely upon the which corresponds to a surface speed of 258 surface feet
enamel covering of the wires in the winding, not only per minute for the same 6.563 inch diameter rotor.
reduces the component cost of producing the coil con 10 Again the magnitude of the spark voltage was adequate
cerned, but also reduces the amount of time required to for engine ignition. Therefore the combination of the
wind the coil. coil assembly of the preferred embodiment and the
Furthermore the physical size of such a winding circuit of the preferred embodiment clearly produces a
without paper of insulation interleaving is reduced. very superior result in that starting occurs at 150
Accordingly the self-capacitance of the winding is re 15 R.P.M. for a moderately sized rotor which is a very low
duced and this reduction improves the electrical char starting speed indeed.
acteristics of the coil. Although the abovementioned rotor revolutions have
It is to be understood that the winding carrying been
spools of the present invention may be used in addition poses converted
of
into rotor surface speeds for the pur
comparison and further details of performance
to conventional windings, if desired, and also may be 20 to be given hereinafter are also quoted in terms of rotor
located coaxially with other windings as the conven
tional coaxial windings of FIGS. 32, 33, 34 and 35. For surface speed, it is to be understood that the physical
construction method, overall size and application to
example, a conventional primary winding 16 may have which the internal combustion engine is to be put, pre
a spool 32 located coaxial with it and exterior to it, the clude the use of large diameter magneto rotors in order
spool 32 carrying the secondary winding. 25
to get high rotor surface speeds for low engine revolu
The problems associated with mechanical breaker
point ignition systems have resulted in the development tions. For example, the rotor of a magneto designed for
use in a hand-held chain saw typically has a diameter in
of electronic ignition systems such as that described in the vicinity of 3 to 5 inches and it is not a practical
U.S. Pat. No. 3,878,452 and assigned to Robert Bosch proposition to “halve' the starting speeds of conven
G.m.b.H. This electronic ignition system is commer 30
cially available as a Bosch electronic ignition circuit tional ignition systems by "doubling' the diameter of
the magneto rotor in order to achieve a high rotor sur
type 525 1/217/280/032 and has a Bosch magneto igni face speed.
tion coil assembly tape 523/60 2204/222/053 which In the above-described tests the secondary voltage
comprises primary and secondary windings designed produced by the Bosch coil assembly when triggered by
specifically for the ignition circuit. The lastmentioned 35 the Bosch circuit at 1,100 R.P.M. was 19 kV whereas
Bosch magneto ignition coil assembly is associated with the secondary voltage produced by the coil assembly of
a magneto rotor having a diameter of 3.3125 inches. the preferred embodiment of the present invention
When the abovementioned Bosch electronic ignition
circuit and magneto ignition coil were both fitted to a when triggered by the abovementioned Bosch circuit at
Husqvarna brand chain saw, a magneto rotor speed of 40 300 R.P.M. was 12.5 kV. Both the Bosch coil assembly
the order of 1,100 R.P.M. was required to start the and the coil assembly of the preferred embodiment of
motor. At speeds below this figure the motor would not the present invention produced a secondary voltage of
start. For the stated diameter of the magneto rotor and 10 kV, at 350 and 150 R.P.M. respectively, when trig
the stated starting magneto rotor revolutions this corre gered by the circuit of the preferred embodiment of the
sponds to a surface speed for the magneto rotor at start 45 present invention. However, a secondary voltage of 10
ing of 955 surface feet per minute. kV is an entirely adequate secondary voltage, will oper
However, when the circuit of FIG. 3 was connected ate most internal combustion engines under most condi
to replace the abovementioned Bosch electronic igni tions, and forms a convenient laboratory reference stan
tion circuit, the same engine started at 350 R.P.M. dard. In addition the secondary voltages created with
which corresponds to a surface rotor speed of 304 sur 50 the coil assembly of the preferred embodiment increase
face feet per minute. It will therefore be seen that the more slowly with increasing engine running speeds than
ignition circuit of the present invention considerably do conventional coil assemblies. A small increase is
improves the starting speed of the engine even when desirable since it protects the coil assembly from possi
used with the magneto coil assembly manufactured by ble insulation breakdown caused by corona discharge.
Bosch. 55 The coil assembly of the preferred embodiment of the
When the preferred embodiment of the magneto coil present invention was compared with the coil assem
assembly of the present invention, to be described in blies produced by other manufactures which are set out
more detail hereinafter, was used in a test apparatus in in Table I hereto. The coil of the preferred embodiment
combination with the abovementioned known Bosch is labeled coil No. 1 in Table I and the abovementioned
electronic ignition circuit, the performance of the elec Bosch coil is labeled No. 3. Only these coils were manu
tronic ignition circuit was also improved. In this case factured specifically for use with an electronic ignition
the diameter of the magneto rotor was 6.563 inches and circuit which does not include mechanical breaker
the abovementioned Bosch electronic ignition circuit points, whilst the remaining coils were all manufactured
first produced a spark from the coil secondary winding for use with conventional ignition systems.
at 300 R.P.M. which corresponds to 516 surface feet per 65 The meaning of the heading for each column of Table
minute for the rotor concerned. The magnitude of the I is as follows.
spark voltage was adequate for engine ignition. It will Np-the number of turns in the primary winding of
therefore be seen that the preferred embodiment of the the coil.
 4,163,437
25 26
Dp-the diameter in decimals of an inch of the wire larly advantageous in starting internal combustion en
used in the primary winding. gines at low revolutions since a high rate of change of
Lp-the inductance of the primary winding in milli primary current is required to produce a high rate of
Henries measured at 40 Hz. change of flux in the coil and hence a secondary voltage
Rp-the resistance of the primary winding in ohms. of sufficient magnitude to create a spark.
Ns-the approximate number of turns in the second As mentioned previously when the magnets in the
ary winding of the coil. rotor pass the coil a voltage pulse is generated within
Ds-the diameter in decimals of an inch of the wire the coil. FIG. 42 illustrated the magnitude of the posi
used in the secondary winding of the coil. tive peak of the voltage pulse as a function of rotor
Rd-the diameter of the rotor in inches. O speed. However, FIG. 44 illustrates the peak power
R.P.M./S.F.P.M.-the number of magneto rotor delivered to a 1.5 ohm resistor directly connected
revolutions per minute for each surface foot per across the primary winding as a function of rotor speed.
minute of rotor surface speed. . This peak power has been calculated by measuring the
Ma-the area in inches of the magnetic pole(s) of the peak of the voltage pulse appearing across the 1.5 ohm
rotor in inches squared. Note that the dimensions 15 resistor, squaring this value and then dividing by the
given are chord distances and not distances along resistance.
the curved surface of the rotor. The number in It will be seen that the peak power produced by the
brackets is the number of separate magnets in the coil of the preferred embodiment exceeds that produced
rotor.
La-the cross-sectional area in inches squared of the 20
by the other coils for all rotor speeds and that the rate
leg or member of the permeable core upon which of change of power produced by the coil of the pre
the primary and secondary windings were ferred embodiment for a given change in rotor speed is
mounted. in excess of that produced by the other coils for all rotor
speeds.
All the coils with the exception of coil No. 6, manu Consideration of the various values given for the coils
factured by Briggs and Stratton, were coils of standard 25
listed in Table I indicates that with the exception of coil
configuration wound on a permeable core as illustrated No. 6, the inductance of the primary winding of the coil
in FIGS. 32, 33 or 34. However, coil No. 6 manufac of the present invention is considerably less than the
tured by Briggs and Stratton was of the configuration corresponding inductances of the other coils. Coils 2 to
illustrated in FIG. 35. The air gap between the magneto 5 all have approximately 200 turns in the primary wind
rotor and coil core for all examples was approximately 30
0.010 to 0.008 inches. ing and inductances ranging between just over 3 to just
Turning now to FIG. 42 of the drawings, shown under 4 mH. However, the coil of the preferred em
therein is a graph of the peak open-circuit primary volt bodiment has only 140 turns in the primary winding but
age of each of the coils listed in Table I against the rotor a considerably reduced inductance of only 2 mH. It is
speed in surface feet per minute of the corresponding 35 apparent that coil No. 6 manufactured by Briggs and
rotor. It will be observed that each such graph of peak Stratton also has a primary winding inductance of 2
open-circuit primary voltage is substantially propor mH, however, this coil only has 75 turns in the primary
tional to the rotor speed, as is to be expected, and that winding.
the characteristic of coils Nos. 1 and 2 are substantially It is generally accepted that for coils having substan
identical and similar to the other characteristics. tially the same physical construction and size, the induc
However, whilst the peak short-circuit current char tance of the coil is proportional to the number of turns
acteristics illustrated in FIG. 43 of the drawings for in the coil squared. Clearly since coil No. 1 has approxi
mately twice the number of primary winding turns but
coils Nos. 2 to 7 listed in Table 1, are similar and pro its inductance is the same as and not four times the
duce a saturation short-circuit primary current in the inductance of coil No. 6, then the different permeable
vicinity of 2 to 3 Amps, the peak short-circuit primary 45
current characteristic of the coil of the preferred em core arrangement for coil No. 6 clearly influences the
bodiment, No. 1, is markedly different from the other inductance measurement. However, consideration of
characteristics. FIGS. 42, 43 and 44 clearly establishes that coils 1 and
In particular the saturation current of the coil of the 6 are markedly different in their properties notwith
preferred embodiment of the present invention is in 50 standing the fact that the primary windings of the coils
excess of 5 Amps which is approximately twice that of have the same inductance.
the other coils. Thus if the coil of the preferred embodi It is believed that the inductance plays a part in the
ment were used with mechanical breaker points, the effectiveness of the coil when used with semi-conductor
points would be burnt out very quickly because of ex ignition systems. From a consideration of FIG. 6 it will
cessive current. In addition the change in short-circuit 55 be seen that the voltage appearing across the primary
primary current for coil No. 1 for a given change in winding increases very dramatically in a short space of
rotor speed, at low rotor speeds, is very much greater time, to the switched voltage Vs, at the moment that the
for coil No. 1 than it is for the remaining coils. This may current flowing in the primary winding is interrupted.
be easily seen by considering the gradient of the tangent Since this interruption takes place with a semi-conduc
line AA shown in FIG. 3. This tangent has a slope tor device, it is important that, when the interruption is
which corresponds to a change in short-circuit primary intended to occur, in fact the primary winding current
current of approximately 40 mA for every unit surface does cease to flow. ki,
foot per minute change in the rotor surface speed. Simi The magnitude of the peak, voltage Vs is believed to
lar tangents for the curves of coils Nos. 2 to 7 have be determined by the product of the inductance of the
slopes which are only approximately one-half the slope 65 primary winding and the rate of change of primary
of the line AA of FIG. 43. The high rate of change of winding current. Therefore if the primary winding has
short-circuit primary current with change in rotor a large inductance this will produce a large magnitude
speed of the coil of the preferred embodiment is particu for the switched voltage Vs.
 4, 163,437
27 28
The collector-emitter conduction path of any transis tion system to be provided which has significantly im
tor device connected in series with the primary winding proved performance.
and acting as a switch essentially comprises 2 semi-con Since the coil assembly of the present invention pro
ductor diodes back-to-back. Therefore even in the ab duces such a low switched voltage Vs it is possible to
sence of any base current, the transistor will conduct 5 use a monolithic integrated circuit as the ignition circuit
current between collector and emitter if a sufficient which is operated by the coil assembly. This has two
driving voltage is applied between the collector and important consequences, firstly the cost of the ignition
emitter to break down one of the abovementioned back circuit is greatly reduced and secondly high gain tran
to-back diodes and allow the transistor to conduct. sistors are able to be used, either as separate devices or
Clearly if such a break down occurs at the time when 10 within an integrated circuit.
interruption to the primary winding current is desired, The results of the first consequence include not only
then the primary winding current will be initially inter cheaper construction costs for the circuit but also a
rupted, and the back emf induced in the primary wind smaller and more reliable circuit. However, the result of
ing then results in a sharp voltage increase. If this in 15 the use of high gain transistors affects the performance
creased voltage is sufficient to cause the transistor to ofAs the combination of coil assembly and circuit directly.
conduct again, then an effective interruption to the when explained above starting at low speed is achieved
primary winding current will not have been achieved. exceedsthea current produced by the primary winding Ip
predetermined level, It, at which transistor
The result of such an ineffectual interruption is a low
induced voltage in the secondary winding because the 20 T2 turns on. If transistor T2 is a high gain transistor this
current flowing in the primary winding will not have a means that the magnitude of the predetermined level of
It is effectively lowered. As a result starting is achieved
high rate of change of flow.
In addition, since the voltage rating of the transistor at lower speeds since only a smaller primary winding
will have been exceeded at each interruption to the current need be generated to cause ignition.
primary winding current, the life of the transistor de 25 byThe coils of the present invention are characterized
vice will be extremely limited and the device will fail in areamounted
primary winding inductance of less than 3 mH and
in an ignition coil assembly in which the
a very short period of time. In order to overcome such
failures in transistor ignition circuits which have previ magnetically permeable core of the assembly only par
ously been operated from conventional coil assemblies, tially encloses the coils thereby leaving at least one side
it has been necessary to use a switching device which 30 of the coils free of the permeable core. Preferably the
has a very high voltage rating. Accordingly such a number of turns in the primary winding lies between 50
and 150 turns. The diameter of the primary winding
device is extremely expensive when compared with wire may vary between 0.003 to 0.045 inches.
lower rating devices which are very much cheaper to Furthermore the coils of the present invention when
purchase than the difference in the voltage rating would operated in conjunction with a megneto rotor are char
suggest at first sight. acterized by the production of high magnitude peak
The switched voltage produced by each of the coil 35 short-circuit saturation primary currents and by rapid
assemblies of Table I when operated at a rotor speed of rates of change for peak short-circuit primary currents
1,000 S.F.P.M. with the circuit illustrated in FIG. 3 is for changes in magneto rotor speed at low rotor speeds.
set forth as follows.
In addition, the coils of the present invention are further
characterized by their ability to deliver high peak pow
Coil No. 1 2 3 4 5 6 7 ers to resistive loads.
Ws, 125 200 220 180 180 170 300 In particular it will be apparent from FIG. 43 of the
drawings, that the coil assemblies of the present inven
tion would be quite unsuitable for use with conventional
It will be seen that the switched voltage induced in 45 mechanical breaker point ignition systems since the
the primary winding of the coil assembly of the pre high primary currents produced on closure of the points
ferred embodiment is considerably below that of the of such a system would quickly burn the points during
other coil assemblies and therefore lower cost semi-con operation and result in very limited operating life for
ductors may be used in conjunction with the coil assem the points.
blies of the present invention. 50 Another advantage of the coil assembly of the present
It will also be seen that coil No. 6, although it has a invention is that the high primary currents produced
low primary winding inductance, because of the config provide power to operate the circuits of the type illus
uration of the permeable core of the coil, produces a trated in FIGS. 24, 25, 26 and 28. In addition, the cur
switched voltage Vs which is comparable with the rent characteristic shown in FIG. 43 is of assistance in
other coils having higher primary winding inductance. 55 operating automatic advance ignition circuits of the
Accordingly coil No. 6 is not suitable for use with tran type illustrated in FIG. 13.
sistor switching devices having low voltage ratings. In order to construct the above-described coil of the
From the foregoing it is apparent that the coils of the preferred embodiment the following empirical proce
present invention, when used in conjunction with elec dure was adopted. A number of hand wound laboratory
tronic ignition systems both of known and novel circuit prototype coils were constructed so as to be suitable for
design, significantly reduces the starting speed able to a conventional magneto rotor and the laminated core
be attained by the magneto ignition system. In addition, illustrated in FIG. 32. A number of different wire thick
the coils of the present invention produce a low nesses were selected for the primary winding ranging in
switched voltage Vs and therefore enable electronic thickness between 0.003 and 0.045 inches. The number
ignition systems having low cost semi-conductor 65 of turns in the primary winding for each coil was varied
switching devices to be used without damage at any between the limits of approximately 50 and 150 turns.
speed especially at high engine revolutions. The combi A substantially standard secondary winding was con
nation of these two features enables a lower cost igni structed having an internal diameter sufficient to ac
 4,163,437
29 30
commodate the various different sizes of primary wind inches and 12,500 secondary turns were selected as the
ings. The preferred form of secondary winding com winding combination to be used in the construction of a
prised 12,500 turns of wire having a thickness of 0.0024 run of identical production coils.
inches. The above-described preferred embodiment of For economic reasons relating to the cost of produc
the ignition circuit of the present invention illustrated in 5 tion and the cost of preparing the necessary machinery
FIG. 3 was then operated from a magneto coil assembly prior to manufacture, only the single abovementioned
including, in turn, each combination of the various pri winding combination was selected for the manufacture
mary windings and the standard secondary winding. of a number of production coils, each having the lami
The rotor R.P.M. required to produce a specified sec nated core illustrated in FIG. 32. The performance of
ondary winding sparking voltage was then recorded for 10 each of the production coils was identical and has been
each wire gauge and each selected number of primary described above in relation to coil No. 1 of Table I. It
turns. The rotor, magnet poles, and laminations de will be seen that the performance of the coil manufac
scribed in connection with coil No. 1 in Table I were tured by production techniques was increased above the
used in each case. The specified sparking voltage se performance produced by the best hand-wound proto
lected as a laboratory reference was 10 kV for the 15 type coil having the same winding combination.
above-described secondary winding, however, the Production coils produced in accordance with the
magnitude of the secondary voltage was able to be present invention have proved capable of producing
increased or decreased by respectively increasing or secondary voltages in excess of 32 kV at 220R.P.M. and
decreasing the number of turns in the secondary wind 40 kV at 500 R.P.M. These results were obtained with
ing. 20 coils having 140 primary turns and in excess of 12,500
It was found that for each gauge of primary wire secondary turns.
thickness, a particular number of turns produced a mini The foregoing describes only some embodiments of
mum number of revolutions required to produce the the present invention and modifications, obvious to
specified secondary voltage. Increasing or decreasing those skilled in the art, may be made thereto without
the number of primary turns away from this specified 25 departing from the scope of the present invention.
TABLE I
Coil Brand R.P.M./
No. Part No. Np Dp Lp Rp Ns Ds Rd S.F.P.M. Ma La
1 Solo 140 0.025 2.0 0.67 12,500 00024 6,563 1.719 0.675 x 1.015 0.445 x 0.500
0.685 0.223
(2)
2 Victa 195 0.025 3.93 0.99 7,000 0.0024 6.563 1.719 0.675 x 1.015 0.445 x0.500
5-183 0.685 0.223
(2)
3 Husqvarna 195 0.024 3.51 0.86 11,550 00012 3.3125 0.868 0.490 x 0.755 0.355 x 0.365
(Bosch) O 0.370 0.30
523/60 0.0014 (2)
2204/222/053
4 McCulloch 200 0.020. 3.02 0.97 10,050 00023. 3.5 0.917 0.510 x 0.900 0.365 x 0.375
(Phelon) 0.459 0.137
(2)
5 Wico 190 0021 3.13 0.83 10,350 00016 4.5 1.18 0.800 x 0.550 0.365 x 0.380
0.440 0.139
(2)
6 75 0.027 2.0 0.49 4,400 0.0024 5.75 1.506 0.725 x 0.445 x 0.500
Brig- 2,000
gs &
Stratton 450 0.223
(1)
7 Solo 300 0.0145 9.53 2.33 11,800 0.0015 3.563 0.933 0.950 x 2.025 0.160 x 0.400
(Bosch) 1924 0.064
Type 411 (2)
2/204/210013

number of turns in both cases increased the R.P.M.

required to produce the specified secondary voltage. We claim:
For example, for a primary winding wire of thickness 1. An ignition circuit for an internal combustion en
0.040 inches both 120 and 140 primary turns produced a gine having a coil assembly including a primary wind
secondary voltage of 10 kV at 400 R.P.M. However, 55 ing with two ends and a magnet carrying rotor rotatable
the specified reference voltage of 10 kV was produced by said engine past said primary winding, said ignition
at 350 R.P.M. for 130 primary turns. Similarly for pri circuit comprising:
mary winding wire having a thickness of 0.025 inches, a first and second transistors, each having a collector, a
primary winding having 130 turns required 450R.P.M. base and an emitter, the collector of the first tran
to produce the desired 10 kV, a primary winding having sistor being directly connected to one end of said
150 turns required 350R.P.M. to produce the secondary primary winding and the emitter of the first transis
reference voltage of 10 kV, but a primary winding hav tor being directly connected to the other end of
ing 140 turns only required 310 R.P.M. to produce the said primary winding, the second transistor having
same secondary reference voltage of 10 kV. its collector-emitter conduction path connected in
Since 310 R.P.M. was the lowest speed achieved with 65 parallel with the base-emitter conduction path of
the hand-wound laboratory prototype coils; 140 pri said first transistor;
mary turns and a primary winding gauge of 0.025 inches a first resistor connected between base and collector
together with a secondary winding gauge of 0.0024 of the first transistor;
 4, 163,437
31 32
a potential divider directly connected across the ends tors, the base of said second transistor being connected
of said primary winding, and the base of said sec to the junction between said series connected resistors.
ond transistor being connected to a point of inter 10. The circuit as claimed in claim 9 wherein a series
mediate potential on said potential divider wherein connected resistor and capacitor are connected between
rotation of said rotor induces a voltage between the the base of said second transistor and the collector of
ends of said primary winding to cause said first said first transistor.
transistor to conduct current from said primary 11. The circuit as claimed in claim 9 wherein a capaci
winding directly through the collector-emitter tor is connected between base and emitter of said sec
conduction path of said first transistor, said second ond transistor.
transistor being turned on by said intermediate 10 12. The circuit as claimed in claim 2 wherein said
potential to turn said first transistor off when said potential divider includes at least one thermistor.
current exceeds a predetermined value. 13. The circuit as claimed in claim 2 wherein the
2. An ignition circuit for an internal combustion en resistance value of said first resistor is dependent upon
gine having a coil assembly including a primary wind temperature.
ing with two ends and a magnet carrying rotor rotatable 15 14. The circuit as claimed in claim 2 wherein said
by said engine past said primary winding, said ignition primary winding includes a tapping intermediate said
circuit comprising: ends and the collector of said first transistor is directly
first and second transistors, each having a collector, a connected to said tapping only at high engine revolu
base and an emitter, the collector of the first tran tions by a switch operatively responsive to engine revo
sistor being directly connected to one end of said 20 lutions.
primary winding and the emitter of the first transis 15. The circuit as claimed in claim 2 wherein one
tor being directly connected to the other end of terminal of a capacitor is connected to the emitter of
said primary winding, the second transistor having said first transistor, the other terminal of said capacitor
its collector-emitter conduction path connected in is connected via two series connected diodes having
parallel with the base-emitter conduction path of 25 like polarity to the base of said second transistor, the
said first transistor; polarity of said two series connected diodes being the
a first resistor connected between base and collector same as the polarity of the base-emitter junction of said
of the first transistor; second transistor, a resistor connected in parallel with
a potential divider directly connected across the ends said capacitor, and a series connected diode and zener
of said primary winding, and the base of said sec 30 diode having opposed polarity connected between the
ond transistor being connected to a point of inter collector of said first transistor and said other terminal
mediate potential on said potential divider wherein of said capacitor, the direction of forward conduction
rotation of said rotor induces a voltage between the of said Zener diode being the same as the direction of
ends of said primary winding to cause said first conduction of the collector-emitter conduction path of
transistor to conduct current from said primary 35 said first transistor.
winding directly through the collector-emitter 16. The ignition circuit as claimed in claim 2 wherein
conduction path of said first transistor without said the maximum short circuit current in said primary
first transistor being saturated, said second transis winding produced by high speed rotation of said rotor
tor being turned on by said intermediate potential is in excess of 4 amps.
to turn said first transistor off when said current 17. The ignition circuit as claimed in claim 16
exceeds a predetermined value. wherein at rotor speeds less than 200 surface feet per
3. The circuit as claimed in claim 2 wherein a diode is minute the rotor speed rate of change of short circuit
connected between said potential divider and the base primary winding current is in excess of 30 mA per sur
of said second transistor to effectively raise the magni face foot per minute.
tude of said intermediate potential, the polarity of said 45 18. The ignition circuit as claimed in claim 2 wherein
diode and the polarity of the base-emitter junction of said primary winding has an inductance of less than 3
said second transistor being the same. mH, is mounted on a magnetically permeable core
4. The circuit as claimed in claim 3 wherein said which passes through the centre of said primary wind
potential divider comprises two series connected resis ing and which only partially encloses said coil assembly
tors and a series connected diode. 50 so as to leave at least one side thereof which is not
5. The circuit as claimed in claim 2 wherein said first adjacent a portion of said core.
transistor comprises a Darlington pair. 19. The ignition circuit as claimed in claim 16
6. The circuit as claimed in claim 2 wherein a diode is wherein said primary winding has between 50 and 150
connected between the ends of said primary winding, turns.
the polarity of said diode being opposed to the collec 55 20. The ignition circuit as claimed in claim 18
tor-emitter conduction path of said first transistor. wherein said primary winding has between 50 and 150
7. The circuit as claimed in claim 2 wherein a zener turns.
diode is connected between the ends of said primary 21. The ignition circuit as claimed in claim 2 wherein
winding, the direction of forward current conduction of the magnitude of said induced primary winding voltage
said zener diode being opposed to that of the collector 60 causes said first transistor to repeatedly conduct pri
emitter conduction path of said first transistor. mary winding current without being saturated, and said
8. The circuit as claimed in claim 2 wherein a resistor intermediate potential turns said second transistor on
and series connected Zener diode are connected be each time said current exceeds said predetermined value
tween base and emitter of said first transistor, the polar thereby resulting in multiple ignition.
ity of said zener diode being opposed to the polarity of 65 22. The circuit as claimed in claim 2 wherein the base
the base-emitter conduction path of said first transistor. of said second transistor is directly connected to the
9. The circuit as claimed in claim 2 wherein said point of intermediatek potential on the potential divider.
potential divider comprises two series connected resis k k six k