Low speed ignition system

A capacitor discharge type ignition system for an internal combustion engine has a secondary charge coil mounted on a ferromagnetic core adjacent to a primary charge coil and an ignition coil, and means for selectively providing current from a battery to the secondary charge coil to increase the charging of a capacitor with the fly back voltage of the secondary charge coil when the current supplied to it from the battery is interrupted or terminated to increase the charge stored by the capacitor at low engine speeds and thereby facilitate starting an engine at very low engine speeds. The battery provides additional energy necessary to provide ignition and starting of the engine at very low engine speeds and can also be used to provide power for other functions, such as to electric starting of the engine, or to power other auxiliary features of the machine powered by the engine. Advantageously, the secondary charge coil is not regulated and excess power discharged from the secondary charge coil is directed to the battery to recharge the battery and maximize its life.

FIELD OF THE INVENTION 
This invention relates generally to ignition systems and more particularly 
to a capacitor discharge-type ignition system for internal combustion 
engines. 
BACKGROUND OF THE INVENTION 
Capacitor discharge-type ignition systems have been used to start spark 
ignited internal combustion engines. Generally, these ignition systems 
have a stator assembly with an ignition coil having primary and secondary 
windings and a charge coil received around a ferromagnetic core. A 
permanent magnet assembly mounted on a flywheel of the engine generates 
pulses within the charge coil as the permanent magnet is rotated past the 
ferromagnetic core. The current pulses produced in the charge coil are 
used to charge a capacitor which is subsequently discharged through the 
primary winding to induce a current in the secondary winding sufficient to 
cause a spark across a spark gap of a spark plug to ignite a fuel and air 
mixture within an engine cylinder combustion chamber to power the engine. 
Examples of capacitor discharge type ignition systems are disclosed in U.S. 
Pat. No. 5,392,753 and U.S. Pat. No. 3,911,887. In these systems, a 
somewhat high engine speed must be obtained before sufficient current 
pulses are generated in the charge coil and transferred to the capacitor 
to charge the capacitor sufficiently such that when discharged, a spark is 
generated across the spark gap of a spark plug. Thus, these prior ignition 
systems have a relatively high minimum rotary speed at which the ignition 
system will produce a spark in the gap of the spark plug to start the 
engine. 
SUMMARY OF THE INVENTION 
A capacitor discharge type ignition system for an internal combustion 
engine has a secondary charge coil mounted on a ferromagnetic core 
adjacent to a primary charge coil and an ignition coil, and means for 
selectively providing current from a battery to the secondary charge coil 
to increase the charging of a capacitor with the fly back voltage of the 
secondary charge coil when the current supplied to it from the battery is 
interrupted or terminated to increase the charge stored by the capacitor 
at low engine rotary speeds and thereby facilitate starting an engine at 
very low engine cranking rotary speeds. The battery provides additional 
energy necessary to provide ignition and starting of the engine at very 
low engine speeds and can also be used to provide power for other 
functions, such as electric starting of the engine, or to power other 
auxiliary features of the machine powered by the engine. Advantageously, 
the secondary charge coil is not regulated and excess power discharged 
from the secondary charge coil is directed to the battery to recharge the 
battery and maximize its life. 
Objects, features and advantages of this invention include providing a 
capacitor discharge ignition system which improves starting of an engine, 
permits starting the engine at low engine cranking speed, provides a 
battery which may be used to power auxiliary functions, recharges the 
battery to extend its life, is of relatively simple design and economical 
manufacture and assembly and in service has a long, useful life.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring in more detail to the drawings, FIGS. 1 and 2 illustrate an 
ignition system 10 embodying this invention which enables starting an 
engine at a very low cranking rotary speed. The system 10 has a permanent 
magnet assembly 12, a stator assembly 14 and associated circuitry. The 
stator assembly 14 has a secondary charge coil 16 adjacent to a primary 
charge coil 18 and an ignition coil 20 all received on a ferromagnetic 
core 21. At low engine rotary speed, the circuitry selectively provides 
current from a battery 22 to the secondary charge coil 16 to increase the 
charging of an ignition capacitor 24 by the fly back voltage of the 
secondary charge coil 16 when the current supplied to it from the battery 
22 is interrupted or terminated to increase the charge stored by the 
capacitor 24 at low engine speeds and thereby facilitate starting the 
engine at very low engine speeds. 
The permanent magnet assembly 12 is disposed on a flywheel 28 which in turn 
is attached to and rotatable in unison with a shaft 30, such as a 
crankshaft or camshaft, of an internal combustion engine. The permanent 
magnet assembly 12 is located at a predetermined angular position relative 
to a key 32 on the shaft 30 which couples the shaft 30 to the flywheel 28. 
Thus, as the shaft 30 rotates the permanent magnet assembly 12 moves past 
a given point in timed relation to a physical position of the shaft driven 
by the engine. Preferably, rotation of the magnet assembly relative to the 
stator assembly 14 is in timed relation to the top dead center position of 
a piston within an engine cylinder to the control the timing of an 
ignition spark relative to the top dead center position of the piston. The 
timing of the ignition system 10 is controlled by circuitry on a printed 
circuit board 34 preferably carried by the stator assembly 14. 
The magnet assembly 12 has a permanent magnet 36 disposed with its poles 
oriented to engage a pair of ferromagnetic pole pieces 38,40. Since the 
flywheel 28 is made of a non-magnetic material, such as aluminum, the 
magnetic flux emitted by the permanent magnet 36 will be concentrated in 
the pole pieces 38,40 for magnetic coupling to the core 21 of the stator 
as the permanent magnet 36 is rotated past the core 21. 
As shown in FIG. 1, the stator assembly 14 is mounted adjacent to the 
flywheel 28 for communication with the permanent magnet assembly 12. The 
stator assembly 14 has a coil bobbin 42 with multiple compartments or bays 
in which the primary charge coil 18, secondary charge coil 16 and primary 
and secondary windings 44,46 of the ignition coil 20 are received. The 
core 21 has a bight or cross bar portion 48 interconnecting a pair of leg 
portions 50,52 extending towards the flywheel 28. The core 21 will 
generally have either two or three leg portions and, in any event, it is 
preferably of a multi-laminar construction of ferromagnetic material such 
as iron plates. 
The coil bobbin 42 has a pair of spaced apart flanges 54 between which the 
primary charge coil 18 and secondary charge coil 16 are co-wound. For 
close magnetic coupling with the permanent magnet assembly 12, the primary 
charge coil 18 and secondary charge coil 16 are disposed adjacent to the 
flywheel 28 to be in close proximity to the permanent magnet assembly 12. 
The secondary winding 46 of the ignition coil 20 is wound between a set of 
closely spaced flanges 56. The primary winding 44 of the ignition coil 20 
is received in a central compartment 58 of the bobbin 42 generally 
radially inwardly of and spaced from primary charge coil 18, secondary 
charge coil 16 and the secondary winding 46. The primary winding 44 of the 
ignition coil 20 is spaced from the primary charge coil 18 and the 
secondary charge coil 16 to minimize the magnetic coupling between them. 
The secondary winding 46 of the ignition coil 20 is fitted closely 
adjacent the primary winding 44 for maximum inductive coupling between the 
primary and secondary windings 44,46 and is connected to a spark plug 60 
and ground 62 as shown in FIG. 2. As is conventional in the art, the 
various coils 16,18,20 and the circuit board 34 are disposed in a plastic 
cup-shaped housing 62 and are encapsulated in a suitable epoxy resin for 
moisture and weather-proofing, enhanced performance and maximum service 
life of the system. 
At low engine speeds it is not advantageous and may be destructive to the 
engine starter to fire the spark plug 60 before the piston has passed its 
top dead center position. Combusting the fuel in the engine cylinder 
before the piston has reached top dead center can cause the piston to stop 
and possibly reverse direction. If this happens while the starter is 
engaged the starter may be damaged. To avoid this situation it is 
desirable to delay combustion until after the piston has passed top dead 
center. To ensure that this is the case, a separate sensor 64 is mounted 
angularity displaced from the primary charge coil 18 such that it creates 
an electrical signal or pulse 66 (FIG. 4A) after the piston has passed top 
dead center. This pulse 66 is communicated to a microprocessor 68 on the 
circuit board 34 where, at low engine rotary speeds, it is used to 
initiate the discharge of the ignition capacitor 24. A suitable, 
commercially available microprocessor is a Zilog Z86E08. 
The sensor 64 is preferably carried by the stator assembly 14 spaced from 
the core 21 and detects the permanent magnet assembly 12 on the flywheel 
28 as it rotates by the sensor 64. The sensor 64 may be a coil, hall 
effect, a magnetic restrictive or other magnetically sensitive material or 
device sufficient to generate a signal when the permanent magnet assembly 
12 rotates past the sensor 64. The sensor 64 is preferably mounted on the 
circuit board 34 which has circuitry to receive the signal 66 generated by 
the sensor 64. Alternatively, the sensor 64 may be designed to use 
optical, mechanical or other means of detecting the position of the 
flywheel 28 or the shaft 30. 
An energy storage device, such as a battery 22 and preferably a nickel 
cadmium battery, is located remotely from the stator assembly 14 and is 
connected to the circuit board 34 with a single wire. The second wire from 
the battery 22 is electrically connected to the frame of the engine which 
is connected to the ground 62 of the circuit board 34. Alternatively, the 
battery 22 can be mounted on or adjacent the stator assembly 14 and may 
have both of its wires connected to the circuit board 34. 
The circuitry 74 of the circuit board 34, as shown in FIG. 2, has the 
ignition capacitor 24 which is selectively discharged to generate a spark 
across the gap 76 of the spark plug 60 when sufficient energy has been 
stored in the ignition capacitor 24. The discharge of the capacitor 24 is 
controlled relative to the speed of the engine by the microprocessor 68. 
Generally, a ceramic resonator 78 energized by the microprocessor 68 
provides timing pulses to the microprocessor 68 which counts the pulses to 
determine or control the length of time for an event. Several capacitors 
71, 73 and 75 act as signal filters and several resistors 77, 79 and 8 1 
provide voltage dividers for various reference signals of the 
microprocessor 68. 
For each revolution of the flywheel 28 and hence the permanent magnet 
assembly 12 past the core 21, a positive main pulse 80 and two, negative 
side pulses 82,84 of a smaller magnitude, as shown in FIG. 3A, will be 
generated in the primary charge coil 18. The main pulse 80 is rectified by 
diode 99 and is used to charge the capacitor 24. The two side pulses 82,84 
are, with reference to ground, of positive potential as shown in FIG. 3B 
and are rectified by diode 98, charge capacitor 100 and through the 
connection at pin 102, turn on a voltage regulator 104 and are used to 
energize the microprocessor 68 and also to provide input reference signals 
86,87 (FIG. 3C) for the microprocessor 68 which are formed by the diode 
88, resistors 90 and 92 and capacitor 94. 
At low engine speeds, such as below 700 rpm or some other speed based on 
system design tradeoffs, the primary charge coil 18, does not charge the 
ignition capacitor 24 to a sufficient level to provide enough energy to 
the primary winding 44 to ensure that a spark will be generated across the 
gap of the spark plug 60. To provide adequate energy to generate a spark 
at ultra low engine speeds, the secondary charge coil 16 is co-wound with 
the primary charge coil 18 to provide a magnetic transformer circuit 95. 
This transformer 95, in conjunction with a transistor 97, and the battery 
22 is used to provide additional energy in the ignition capacitor 24 by 
switching the battery current to the secondary charge coil 16, on and off 
such that the ignition capacitor 24 is charged through diode 99 by the 
flyback voltage of the charge coil 16 which is generated when the battery 
current to the secondary charge coil 16 is switched off and which is 
transformer coupled to the primary charge coil 18. The transistor 97 
controls the switching of the current on and off to the secondary charge 
coil 16 and is controlled by the microprocessor 68 through pin 17 and 
resistor 129. The ignition capacitor 24 is protected from over charging by 
diode 101. 
During the 90 to 140 micro seconds that the transistor 97 is turned on, the 
voltage from the battery 22 causes a current to flow in the secondary 
charge coil 16. In one embodiment, this current reaches a maximum of from 
1 to 4 amps. When the transistor 97 is turned off, the current to the 
secondary charge coil 16 is terminated. The voltage in the coil 16 
increases proportionately with the rate of change in the current due to 
the collapse of the magnetic field around the coil 16 induced by the 
current. This collapsing magnetic field is also coupled into the primary 
charge coil 18 co-wound on the same bobbin and ferromagnetic core 21 and 
causes current to flow in the primary charge coil 18 through diode 99 to 
charge the ignition capacitor 24. The time that the transistor 97 is 
turned off must be sufficient for all of the available energy in the 
magnetic field to be transferred into the ignition capacitor 24, and this 
time actually gets shorter as the charge on the ignition capacitor 24 
increases. On each successive cycle, the voltage on the ignition capacitor 
24 is increased by a few volts. During typical operation of a particular 
embodiment of ignition system 10, it takes from 10 to 80 cycles to 
increase the energy stored in the ignition capacitor 24 to a level 
sufficient to ensure proper operation of the spark plug 60. 
During the first revolution of the engine, this charging takes place when a 
leading edge 116 (FIG. 3C) of the first pulse 86 is detected and 
corresponds to the initial pulse block 96, as shown in FIG. 4A, which only 
occurs on the first revolution of the engine and which provides energy for 
an initial discharge of the capacitor. During subsequent revolutions, the 
charging (nominally indicated at block 103 in FIG. 4A) of the capacitor 24 
by the secondary charge coil 16 begins immediately following discharge of 
the capacitor 24 and continues until the microprocessor 68 determines from 
the time between successive pulses 66 that the engine is rotating faster 
than a preprogrammed threshold speed that corresponds with the primary 
charge coil 18 alone generating sufficient energy to charge the ignition 
capacitor 24 and ensure a spark is generated across the gap at the spark 
plug 60 when the capacitor is discharged. Depending on system design, this 
threshold speed the engine is could be as low as 300 rpm or as high as 
1500 rpm. At low engine rotary speeds, pulses 66 are used to time ignition 
to prevent ignition before the engine piston has top dead center which is 
undesirable as discussed above. 
In addition to providing energy for the supplemental charging of the 
ignition capacitor 24, the battery 22 may also be used to provide power 
for other auxiliary functions of the engine or of the machine powered by 
the engine. Advantageously, the system may also recharge the battery 22. 
To minimize system cost and complexity the secondary charge coil 16 is 
used to recharge the battery 22 and desirably, the recharging function is 
not regulated and all excess power is directed into the battery 22 by a 
diode 136. Additionally, excess power from the primary charge coil 18 is 
directed through diode 110 to provide additional charging of the battery 
22. 
The energy delivered to the battery is a function of engine speed. At low 
engine speeds the energy developed by the secondary charge coil 16 does 
not create a voltage greater that the battery voltage plus the forward 
voltage drop of the diode 136. At higher speeds the energy will be great 
enough that the diode 136 will be forward biased and current will begin to 
flow through the diode 136 and the battery 22. The engine speed at which 
this begins to happen is a function of the battery 22 charge state, the 
magnet assembly 12 strength, the gap between the pole pieces 38,40 and the 
core 21, the number of turns of the secondary charge coil 16, and the 
inductance of the charge coil and associated wiring. A representative 
graph of the charging current vs. engine rpm is shown in FIG. 7. 
Operation 
Upon initial cranking of the engine, as shown in FIGS. 4A, 4B and 4C, the 
first passing of the magnet assembly 12 by core 21 generates signal 86 
which triggers the microprocessor 68 to generate a series of pulses 96 of 
sufficient quantity to initially charge the capacitor 24. A portion of the 
energy of the pulse 82 is conducted through a diode 98 to charge a 
capacitor 100 connected to a shutdown control pin 102 of a system voltage 
regulator 104. This turns the regulator 104 on to provide regulated 
voltage from the battery through a diode 106 which is filtered by a 
capacitor 108. As the engine rotary speed increases, the side pulses 82,84 
from the primary charge coil 18 and also the adjacent secondary charge 
coil 16 increase in peak voltage. To provide the operating power for the 
system 10, when the peak voltage of the side pulses 82,84 increases to a 
level greater than the battery voltage plus the voltage drop across the 
diode 110, current flows from the primary charge coil 18 and secondary 
charge coil 16 into the capacitor 108. To conserve the battery power, a 
resistor 112 ensures that if pulses are no longer generated by the primary 
charge coil 18 and secondary charge coil 16, the voltage regulator 104 
will be turned off at least in part to prevent unnecessarily draining the 
battery 22. Also, through a diode 114 the microprocessor 68 has the 
ability to keep the regulator 104 turned on to permit the microprocessor 
68 to control the length of time that the voltage regulator 104 is kept on 
when the engine is running at very low speeds. 
As shown in FIG. 4A, the pulses 66 derived from the sensor 64 as the 
permanent magnet assembly 12 rotates past the sensor 64 are timed to be at 
the proper point of engine rotation at which an ignition spark should be 
provided when the engine is rotating at a very low speed. During the first 
revolution of the engine the microprocessor 68 measures the time between 
leading edges of successive pulses 66. This time corresponds to the engine 
speed. Upon completion of the second revolution and until the completion 
of a revolution whose duration is shorter than a preprogrammed time, the 
engine speed is determined using this method of measuring the time between 
the pulses 66. When an engine revolution occurs having a duration less 
than the preprogrammed time, the ignition system 10 switches to a second 
method of measuring engine speed using the width of the first pulse 86 as 
discussed in greater detail below. 
At higher engine speeds, timing pulses 120, as shown in FIG. 5A, are used 
in the microprocessor 68 and are counted between a leading edge 116 (FIG. 
36) of the first pulse 86 (FIG. 36) and a trailing edge 118 of the first 
pulse 86 as generally indicated at 120. The width of the first pulse 86 is 
a function of the rotational speed of the engine shaft 30 and the flywheel 
28 and the number of timing pulses counted by the microprocessor which 
occur during pulse 120 will be inversely proportional to the rotational 
speed of the engine. The timing pulse counts are used for establishing a 
timing reference used in the microprocessor 68 for controlling (advancing 
and retarding) the spark timing using programmed, or stored data, of the 
most efficient spark advances for various rotational speeds of the 
particular engine on which the system is to be used. Programmed in this 
way and based upon the actual engine rpm, the microprocessor 68 will 
output a control signal 122 which triggers an SCR 124 through the noise 
protection devices: diodes 126; capacitor 128; and resistor 130. 
Additional resistors 127, 129 and 131 act as a voltage divider to protect 
the gate of the SCR 124. When the SCR 124 is triggered by the control 
signal 122 it discharges the capacitor 24 through the primary winding 44 
of the ignition coil 20 and thereby induces a current in the secondary 
winding 46 to generate a high voltage producing spark (nominally 
represented at 133 in FIGS. 4C and 5C) at the spark plug 60. A graph 
representing the maximum spark voltage as a function of engine rpm is 
shown in FIG. 6. The control signal 122 is timed for the most efficient 
spark ignition operation of the engine and is determined based on the 
width of the first pulse 86, and generated as a predetermined time delay 
132 from a leading edge 134 of the second pulse 87 to the generated 
control signal 122. 
When the microprocessor 68 determines from the width of the first pulse 86 
that the engine rotational speed is above another much higher 
preprogrammed maximum engine rotary speed (such as 6,000 to 10,000 rpm) 
the control signal 122 to the ignition SCR 124 may be disabled so that the 
spark will not occur in order to provide over speed protection for the 
engine. This will cause the engine to slow down due to lack of power. On 
subsequent revolutions the microprocessor 68 will monitor the width of 
pulse 86 until it determines that the speed has been reduced to a level 
below this higher preprogrammed speed, it will then re-enable the output 
control signal 122 to fire the spark at the proper time. Pulses 86 are 
used at higher engine speeds as the pulses 66 from the sensor 64 occur too 
late at higher engine speeds to be useful. 
If desired, an engine kill switch 140 may be connected to the circuit at 
terminal 142. When the kill switch 140 is closed by the operator all of 
the charging power that is normally supplied to the ignition capacitor 24 
is shunted to the system ground 62. This prevents energy from being stored 
in the ignition capacitor 24 and subsequently being discharged through the 
primary winding 44 which in turn means that no spark will be generated. 
Lack of an ignition spark will prevent combustion and allow the engine 
system friction to bring the engine to a stop. If the operator releases 
the kill switch 140 before the engine has come to a complete halt the 
engine may continue to run. An option can readily be added to the kill 
function to kill the ignition until the engine has come to a complete 
stop.