Ignition system

An improved ignition system including a member rotatable about an axis and having a permanent magnet with an outwardly extending flux field carried by the member to create a flux field rotating in a given angular path concentric with the axis of the rotating member. In the system there is provided a circuit for creating a sparking voltage upon a rapid change in current in at least a portion of the circuit and switching means for causing the rapid change in current upon actuation of the switching means. The improvement includes a device for storing sparking energy, the switching means includes a solid state device for discharging the storage device upon receipt of a firing signal and a Hall Effect switch activated by a selected D.C. biasing voltage and mounted at a given position with respect to the annular path of the rotating flux field. The Hall Effect switch initiates the switching means to discharge the storage device and cause sparking of the ignition system. Also, there is provided means for limiting the rate of storage of the storage device for limiting maximum speed of an internal combustion engine controlled by the improved ignition system.

This invention relates to the art of ignition systems for internal 
combustion engines and more particularly to an improved ignition system of 
the type having switching means for discharging stored electrical energy 
to create sparking voltage. 
BACKGROUND OF INVENTION 
The present invention is particularly applicable for a single cylinder 
internal combustion engine used in a movable implement such as a power saw 
and it will be described with particular reference thereto; however, the 
invention has much broader applications and may be used in various 
internal combustion engines for a variety of purposes having a various 
number of control spark plugs. 
In the past, the ignition system for hand implements, such as power saws, 
lawn mowers, snow blowers and the like, have used a magneto system wherein 
a rotating flywheel carries a permanent magnet which induces a voltage in 
the primary winding of an ignition coil. Mechanical points then open the 
primary winding circuit at a selected time when the induced voltage has 
caused a high or peak current flow. This collapses the current flow in the 
primary winding and causes a high voltage in the secondary winding of the 
ignition coil. Some prior ignition systems for small engines have used the 
capacitor or induction discharge concept. In the capacitor concept, a 
capacitor is charged to a given voltage and stores electrical energy. 
Mechanical points are then actuated to discharge the stored energy in the 
primary winding of an ignition coil. In this manner, a high sparking 
voltage is created in the secondary winding of the ignition coil to cause 
a spark at the spark plug. These types of systems have been employed in 
various implements driven by single cylinder internal combustion engines. 
These ignition systems have also been used in larger engines having more 
than one cylinder. In each of these instances, mechanical switching is 
required for creating the sparking voltage at the spark plug. Substantial 
effort has been made to completely eliminate mechanical switching in 
ignition systems, primarily for multiple cylinder internal combustion 
engines such as those used in motor vehicles. These systems have used a 
variety of solid state switching arrangements for creating a rapid change 
in current to induce a high voltage at the secondary winding of the 
ignition coil. In many of these systems, an inductive trigger is used to 
discharge the electrical energy. Such a trigger is operated by a moving 
magnetic field driven by the engine. Consequently, the speed of the engine 
determines the firing point which may not be the desired position for a 
discharge system. 
The present invention relates to an improvement in the solid state ignition 
arrangement for a discharge system and primarily to an improvement in such 
a system which is beneficially used in a single cylinder engine although 
applicable to other types of ignition systems. The invention uses no 
mechanical switching for the energy discharge circuit and is operated 
independently of engine speed, although it may be coordinated with engine 
speed. 
THE INVENTION 
In accordance with the present invention, there is provided an improvement 
in an ignition system including a member rotatable about an axis, a 
permanent magnet having an outwardly extending flux field and carried by 
the member to create a flux field rotating in a given annular path 
concentric with the axis, a circuit for creating a sparking voltage in a 
first winding upon a rapid changing current in at least a portion of the 
circuit, and switch means for causing the rapid change in current upon 
actuation thereof. This improvement includes an electrical energy storing 
means in the circuit for storing electrical energy, a Hall Effect switch 
means for periodically discharging, upon actuation, said stored energy 
through a second winding magnetically coupled to the first winding, a 
biasing circuit for directing a D.C. biasing voltage of a selected level 
to the Hall Effect switch, and means for locating the Hall Effect switch 
at a selected position in the path. 
In accordance with another aspect of the invention, the improvement as 
defined above, includes a coil means for directing electrical energy to 
the storing means and means for mounting the coil means in the path to 
receive induced energy upon exposure to the moving magnetic field. In this 
manner, the storage means and the Hall Effect switch means are both 
operated by the same moving magnetic field. 
In accordance with another aspect of the invention, there is provided a 
circuit means for storing energy in the storing means at a selected rate, 
which selected rate is sufficient to store electrical energy to a given 
sparking level when the time spacing of the periodic discharging 
operations of the Hall Effect switch is above a selected amount. In this 
manner, if the time spacing between adjacent discharge operations by the 
Hall Effect switch is below a given level, a sparking voltage is not 
available in the ignition system. This provides an efficient over speed 
control for the internal combustion engine using the improved ignition 
system. 
In accordance with another aspect of the invention, the selected rate of 
storing energy in the storage means is varied. In this manner, the maximum 
speed of the internal combustion engine controlled by the improved 
ignition system is selectively variable. 
In accordance with still a further aspect of the invention, the D.C. 
biasing circuit includes a coil means in the annular path of the moving 
magnetic flux field. In this manner, voltage is induced into the coil by 
the same flux field which controls the charging of the capacitor or other 
storage device and the operation of the Hall Effect switch. This provides 
an efficient manner for performing the total ignition function. 
In accordance with another aspect of the invention, there is provided an 
improvement as defined above, which improvement includes means for 
changing the angular speed of the rotatable member over a given range and 
mechanical means for changing the selected location of the Hall Effect 
switch in the flux path in accordance with the speed change and for at 
least a portion of the speed range. 
The primary object of the present invention is the provision of an improved 
ignition system, which improvement can be used in various internal 
combustion engines and is durable and requires less maintenance than 
systems employing mechanical switching. 
Still another object of the present invention is the provision of an 
improved ignition system, which improvement includes an energy storing 
means discharged periodically by a Hall Effect switch. 
Yet another object of the present invention is the provision of an 
improvement as defined above, which improvement provides an ignition 
system having no mechanical switching and thus reduces wear caused by such 
switching. 
Another object of the present invention is the provision of an improvement 
as defined above, which improvement allows for an over speed limitation in 
an internal combustion engine without requiring moving parts. 
Still a further object of the present invention is the provision of an 
improvement as defined above, which improvement allows for over speed 
limitation in an internal combustion engine without flooding the 
carburetor and effecting ease of subsequent starting. 
Another object of the present invention is the provision of an improvement 
as defined above, which improvement provides a firing position that is not 
determined by a mechanical switch and is independent of engine speed. 
These and other objects and advantages will become apparent from the 
following description.

PREFERRED EMBODIMENT 
Referring now to the drawings, wherein the showings are for the purpose of 
illustrating a preferred embodiment of the invention only, and not for the 
purpose of limiting same, FIGS. 1 and 2 illustrate an appliance A, in the 
form of a chain saw of the type driven by an internal combustion engine 
having a single cylinder. Of course, the invention is applicable to other 
types of internal combustion engines having different number of cylinders, 
as long as a spark plug is required for igniting the combustible mixture 
within the cylinder. An internal combustion engine is schematically 
illustrated as including piston 10 and spark plug 12 connected to the 
ignition system by a wire 14. The spark plug includes two spaced 
electrodes, one of which is shown as electrode 16. The internal combustion 
engine is located within housing 18, which forms the support body of 
appliance A. The ignition system for creating a spark across electrode 16 
includes coil means 20 having core 22 with inwardly facing pole shoes 24 
which are within the path P of rotating magnetic flux field F. Of course, 
other arrangements could be used for inducing a voltage in the coil means 
20 which includes a winding T.sub.1 wrapped around core 22 for receiving 
induced charging voltage as will be explained later. A somewhat standard 
ignition coil 26, shown in FIG. 1 and schematically illustrated in FIGS. 
4-6, includes primary winding T.sub.2, secondary winding T.sub.3 and 
magnetic coupling core 28 of high permeability material, such as soft iron 
laminations. This standard ignition coil structure is used for creating a 
sparking voltage across electrodes 16 of spark plug 12 by wire 14 
extending from the secondary T.sub.3. A carburetor 30 of somewhat standard 
design is controlled by a manually movable link 32 through a connecting 
rod 34. This carburetor controls an intake system illustrated 
schematically in FIG. 1 as including an air filter 38, in accordance with 
standard practice. Accelerator link 40 is controlled by an appropriately 
positioned manually movable trigger to control the setting of carburetor 
30 and thus the requested speed of the internal combustion engine used in 
appliance A. In the illustrated embodiment, arm 42 is fixedly secured onto 
outboard bracket 44. Thus, as an operator depresses the accelerator 
trigger, link 40 controls carburetor link 32 to increase the intake 
through carburetor 30. 
To create the rotating magnetic flux field F travelling in an annular path 
P, there is provided a flywheel 50 having the basic structure of a magneto 
flywheel of the type used in a magneto ignition system. Flywheel 50 thus 
includes a permanent magnet with outwardly facing circumferentially 
extending magnetic poles 50a, 50b properly polarized to produce the 
desired induced voltage within coil means 20 for a purpose to be 
hereinafter described. Flux field F intersects pole shoes 24 of core 22 
for inducing a voltage in the winding T.sub.1 for use in the ignition 
system constructed in accordance with a preferred embodiment of the 
invention. Flywheel 50 is connected to a shaft 52 and is rotatable about 
an axis a. An appropriate arrangement is used for securing flywheel 50 for 
rotation with shaft 52. A variety of structures could be used; however, in 
accordance with the illustrated embodiment, key 54 holds tapered bore of 
flywheel 50 over the tapered end of shaft 52. Nut 56 prevents axial 
movement of the flywheel during operation of appliance A. The illustrated 
appliance includes cover 60 for enclosing the flywheel and ignition system 
of the illustrated embodiment. In accordance with this illustrated 
embodiment, sprocket 62 drives chain 64 supported by chain guide 66 in 
accordance with standard practice in the construction of a chain saw. Of 
course, the environment of the present invention is not important and is 
used for illustrative purposes only. 
Below flywheel 50 there is provided a Hall Effect switch HE having an 
output 70, biasing or power supply terminals 72, 74 and an upper flat 
surface 76. This switch causes the discharge spark when exposed to flux 
field F as will be explained in more detail with respect to the circuits 
of FIGS. 4-6. In accordance with one aspect of the invention, the position 
of switch HE is changed as the engine speed is changed. Various structures 
could be used for this purpose. In the illustrated embodiment, a manually 
movable plate 80 is rotatable about axis a. An opening 81 of plate 80 
surrounds shaft 52 for movement of plate 80 angularly with respect to the 
shaft. An appropriate arrangement is used for allowing selected manual 
movement of plate 80. Various mechanisms could be employed; however, in 
accordance with the illustrated embodiment, circumferentially spaced 
bearing stands 82, 84 and 86 locate and rotatably mount plate 80. These 
stands are illustrated as generally arcuately contoured, U-shaped channels 
with upper and lower ball bearing plates 90, 92 in each of the channels. 
In this manner, plate 80 is rotatable about axis a. As best shown in FIG. 
2, slot 100 having ends 102, 104 coacts with a pin 106 supported on 
bracket 44 to limit the arcuate, or angular, movement of plate 80 with 
respect to axis a of the rotating magnetic field and flywheel 50. Lug 110 
on plate 80 and a fixed pin 112 are connected by a tension, coil spring 
114. This structure spring biases plate 80 into the position illustrated 
in FIG. 2. In this initial position of plate 80, pin 106 engages edge 102 
of slot 100. Plate 80 is used as a mechanical means for manually moving 
Hall Effect switch HE having output 70 and biasing or power supply 
terminals 72, 74. The upper flat surface of switch HE carries the Hall 
cell or chip and when this surface is exposed to a magnetic field, an 
output signal is created in the output 70. As will be explained in 
connection with FIGS. 4-6, the Hall Effect switch, when exposed to the 
magnetic field F, causes firing of a spark across electrode 16 of spark 
plug 12. The angular position of Hall Effect switch HE determines the 
firing position with respect to the angular rotation of flywheel 50 and 
thus the angular position of the crankshaft of the internal combustion 
engine. Thus, the position of the Hall Effect switch in path P of flux 
field F determines the relationship of the spark created at spark plug 12 
and the cycle of the internal combustion engine. By allowing mechanical 
movement of the Hall Effect switch within path P of flux field F, the 
advance and retard position of the created spark can be manually adjusted. 
Various mechanisms could be employed for this purpose; however, in the 
illustrated embodiment, plate 80 is rotated to change the firing position 
of the spark at spark plug 12. In accordance with one aspect of the 
invention, this manual movement of the Hall Effect switch is coordinated 
with the speed of the internal combustion engine. The faster the speed of 
the engine, the more the spark is advanced by moving Hall Effect switch HE 
to the left as shown in FIG. 2. To provide the desired coordination 
between the speed of the engine and the advance of the spark, there is 
provided an interconnecting mechanism, schematically illustrated as a 
spark advance rod 120 having a first end 122 pivotally secured to 
accelerator link 40. The second end 124 of rod 120 is provided with a 
vertical segment 126 extending through an opening 130 in plate 80. This 
opening has a first edge 132 initially engageable by segment 126 and a 
second edge 134. As illustrated, a slidably mounted bias plate 140 is 
movable to the left, as shown in FIG. 2, against the biasing effect of a 
compression spring 142. The distance x is the maximum spacing between 
plate 140 and segment 126 when the accelerator is at the lowest value. 
Thus, as rod 120 is moved to the left, during acceleration of the internal 
combustion engine, vertical segment 126 leaves edge 132. Plate 80 is not 
moved until vertical segment 126 engages plate 140. At that time, the 
spring 142, which has a higher spring constant than spring 114, holds 
plate 140 in the position illustrated in FIG. 2. Thus, the action of 
vertical segment 126 against plate 140 elongates spring 114 to move plate 
80 with pin 106 leaving edge 102. As the position of the accelerator 
continues to increase the speed of the internal combustion engine, 
vertical segment 126 continues to rotate plate 80. This advances the 
position of Hall Effect switch HE until edge 104 of slot 100 engages pin 
106. At that time, plate 80 can move no further in an angular direction. 
Consequently, further movement of lever 40 in the clockwise position, as 
shown in FIG. 1, causes segment 126 and plate 140 to compress spring 142. 
This continued movement of lever 40 causes no further movement of plate 
80. The spark maximum advance is determined by the relative position of 
Hall Effect switch HE with respect to the rotating flywheel 50 when edge 
104 is against pin 106. Consequently, during acceleration of the internal 
combustion engine, the firing point remains constant for a length of 
movement determined by the distance x between vertical segment 126 and 
plate 140. After this movement has been accomplished by link 40, further 
increase in speed of the internal combustion engine increases the advance 
of the spark. After this changeable advance has progressed with further 
increases in speed to the extent determined by the arcuate length of slot 
100, further spark advance does not occur with the increased engine speed. 
This relationship is schematically illustrated in FIG. 3. Of course, the 
advance of the spark by changing the selected position by the Hall Effect 
switch HE can be controlled by the location and arcuate length of slot 100 
together with spacing x, as shown in FIG. 2. As the speed of the internal 
combustion engine is decreased, the reverse action generally takes place 
and the spark is retarded as speed is decreased. The relationship depicted 
in FIG. 3 is illustrative in nature and may be varied in accordance with 
the particular design of the internal combustion engine at the desired 
relationship of the spark with respect to the top dead center of the 
piston 10 as it is operating in the internal combustion engine. Flux field 
F between poles 50a, 50b extends radially outwardly and also radially 
upwardly and downwardly from flywheel 50. Thus, the Hall Effect switch HE 
on plate 80 and below magnet poles 50a, 50b is within the path P of flux 
field F. Of course, the Hall Effect switch could be located in a position 
spaced radially from the periphery of the flywheel by providing a bracket 
on plate 80. However, in practice, the Hall Effect switch is located in 
path P of flux field F and below the peripheral edge of flywheel 50. 
As is well known, a Hall Effect switch is an integrated circuit component 
utilizing the Hall Effect principle to change the voltage at output 70. 
The Hall Effect switch is biased by a 5-20 volt D.C. biasing voltage 
applied across terminals 72, 74. The biasing circuit has a current rating 
of generally 5-20 milliamps. When a Hall Effect switch is subjected to a 
flux field having an intensity above a threshold point, known as the 
"operate point" the output 70 is toggled. This happens substantially 
instantaneous and requires only a few nanoseconds. In many instances, a 
Hall Effect switch has an input voltage regulating stage. In practice, ULS 
3006 T Hall Effect digital switch unit is used. This switch is distributed 
by Sprague Electric Company of Concord, N.H. and includes an input voltage 
regulator to maintain the D.C. biasing voltage substantially fixed to give 
a set flux operate point. When the Hall Effect switch is regulated 
internally, as done in the preferred embodiment of the invention, voltage 
across terminals 73, 74 is a supply voltage which may vary somewhat. 
However, in practice the input voltage is regulated at a voltage, such as 
9 volts D.C. to guarantee a fixed operate point, or at least sufficient 
supply voltage. The flux operate point to toggle switch HE is determined 
by the internal or external D.C. biasing voltage. 
Referring now to FIGS. 4-6, several wiring diagrams are illustrated for use 
in the preferred embodiment of the invention as illustrated in FIGS. 1 and 
2. The preferred wiring diagram is shown in FIG. 4 wherein a storage 
device 200, a capacitor in this instance, is in series with primary 
winding T.sub.2 of ignition coil 26. In this series circuit there is also 
provided a switching means 202 in the form of an SCR having a cathode 206, 
an anode 204 and a gate 208. The SCR has sufficient reverse voltage 
characteristics to withstand any reverse voltage experienced by the 
ignition circuit. Diode 230 also protects the SCR in the circuit 
illustrated in FIG. 4. To charge capacitor 200 there is provided a 
charging circuit 220 including a rectifying diode 222 and a charging 
resistor 224 having a value for charging capacitor 200 to a sufficient 
voltage for periodic firing through SCR 202 at various speeds of the 
internal combustion engine. The SCR is fired, in accordance with the 
invention, by Hall Effect switch HE. The Hall Effect switch, as previously 
mentioned, includes output 70 and biasing or voltage supply terminals 72, 
74. As is well known, output 70 toggles when switch HE is exposed to a 
magnetic flux field exceeding a certain flux intensity. The intensity 
required to toggle output 70 is determined by the D.C. biasing voltage 
applied across terminals 72, 74 or regulated internally of the integrated 
circuit switch. Generally the biasing voltage is a fixed voltage in the 
general range of 5-20 volts D.C. In practice, the biasing voltage is 9 
volts regulated internally of switch HE. However, an external regulated 
voltage of 9 volts is used to supply power to terminals 72, 74. This 
regulated supply can be used with either a regulated or linear, i.e., 
non-regulated, Hall Effect switch. In FIG. 4, flux field F created by the 
magnet having poles 50a, 50b has sufficient intensity to actuate switch HE 
as flywheel 50 rotates the flux field into proximity with the Hall Effect 
switch. A biasing circuit 240 for maintaining the D.C. biasing or supply 
voltage across terminals 72, 74 includes a storage capacitor 242 and a 
Zener diode 244 having a break down voltage, which in practice is 9 volts. 
Rectifying diode 246 is connected with winding T.sub.1 at a tap 248. Thus, 
voltage induced into winding T.sub.1 is rectified by diode 246 and charges 
capacitor 242 which is maintained at 9 volts, or any other selected volts, 
by Zener diode 244. Consequently, D.C. voltage for Hall Effect switch HE 
is constant at a selected value determined by circuit 240. To prevent a 
spark by the circuit illustrated in FIG. 4, there is provided a stop 
switch 254 which grounds terminal 72. At ground potential, switch HE can 
not be toggled by a flux field of the intensity of field F. Thus, no 
output signal can be created at terminal 70 by a flux field F passing 
across switch HE. When flux field F intersects switch HE, an appropriate 
signal is created at terminal 70 to energize line 250 to produce a gating 
signal in line 208. Resistor 252 is a leakage resistor for gate 208 and 
terminal 70. 
In operation, as flux field F passes by shoes 24 of core 22, induced 
voltage is created in charging circuit 220 for charging capacitor 200 to a 
level sufficient to cause a sparking voltage upon discharge through SCR 
202. Consequently, electrical energy is stored in capacitor 200. At the 
same time, coil means T.sub.1 maintains capacitor 242 charged to the 
desired 9 volt D.C. biasing or supply voltage level. Of course, in use, 
capacitor 200 is repeatedly charged and discharged by the SCR to produce 
repeated sparks at plug 12. When flywheel 50 reaches a selected angular 
position, the flux field F triggers switch HE. This gates SCR and 
discharges the stored electrical energy of capacitor 200 through primary 
winding T.sub.2. This rapid increase of current in primary T.sub.2 causes 
a high induced voltage in the secondary winding T.sub.3. Thus, a sparking 
voltage is created across electrode 16 of spark plug 12. Resistor 224 has 
a value to allow sufficient charging of capacitor 200 between periodic 
discharges by the action of Hall Effect switch HE. To stop creation of 
sparks, switch 254 is closed. This removes the D.C. voltage across 
terminals 72, 74 so that there is no additional gating signals from output 
70 to SCR 202. SCR 202 is commutated by the current oscillations in the 
series circuit including winding T.sub.2. 
Referring now to FIG. 5, a modification of the circuit illustrated in FIG. 
4 is presented. In this modification, the biasing or supply circuit 240' 
for Hall Effect switch HE includes a battery 260. Consequently, the 
biasing voltage is not applied by induced voltage in winding T.sub.1. A 
stop switch 262 is opened to remove the D.C. voltage from switch HE. 
During normal operation, switch 262 is closed. Other components of the 
wiring diagram shown in FIG. 5 correspond to the same components used in 
the wiring diagram of FIG. 4. 
Referring now to FIG. 6, a further modified D.C. biasing circuit 240" is 
provided. In this circuit, battery 280 provides a D.C. voltage in a manner 
similar to biasing circuit 240'. In this modified circuit, battery 280 is 
connected in series with a stop switch 286. Combined with this biasing 
circuit is a further circuit similar to biasing circuit 240. A capacitor 
280 and a Zener diode 284 are connected in parallel to receive energy from 
rectifying diode 246. By using this combined structure, the battery 280 
assures a constant 9 volt D.C. biasing voltage across terminals 72, 74 for 
fixed operation of switch HE irrespective of slight variations in the 
voltage received from coil means T.sub.1. This constant voltage can 
provide the fixed D.C. biasing or supply voltage for an internal regulated 
voltage of switch HE. Of course, other arrangements could be used for 
discharging electrical energy stored in a storage device by the operation 
of a Hall Effect switch means. For instance, it is possible to use an 
inductive storage device instead of a capacitive storage device as shown. 
In accordance with another aspect of the present invention, there is 
provided an adjustable over speed circuit having no moving parts and 
requiring no modification of the carburetor for limiting the maximum speed 
of the internal combustion engine controlled by the ignition system. This 
concept is schematically illustrated in FIG. 8 wherein a charging circuit 
300 is used for charging capacitor 200. This charging circuit includes a 
variable resistor or rheostat 302. As shown in FIG. 7, capacitor 200 is 
charged along a standard time constant curve r toward a selected voltage 
E, which is greater than the D.C. voltage required for sufficient energy 
to create a spark upon discharge of the capacitor 200. In the lower 
portion of FIG. 7, a first trigger S.sub.1 discharges capacitor 200. 
Shortly thereafter, the capacitor starts to recharge along curve r. At a 
certain speed illustrated as 7000 rpm, the next adjacent firing trigger 
S.sub.2 is created at a time spaced from the first trigger S.sub.1 by 
time n. At the time of trigger S.sub.2 Hall Effect switch HE discharges 
capacitor 200. Since the capacitor is at a charged level greater than the 
sparking voltage, a spark is created at the spark plug. As the speed of 
the engine increases, fly-wheel 50 has an increased velocity so that 
eventually the next adjacent trigger pulse after a pulse S.sub.1 will be 
in the time relationship position indicated by trigger S.sub.3. This new 
trigger has a time spacing m from trigger S.sub.1. As shown in FIG. 7, 
discharge of capacitor 200 at this position will not cause a spark in the 
internal combustion engine. There is not sufficient energy stored within 
capacitor 200, since the capacitor is below the spark voltage. 
Consequently, by selecting the proper value of resistor 302, a speed 
limiting feature for the engine is accomplished. Above a certain 
rotational speed of flywheel 50, no spark will be created. As the speed is 
decreased, a spark will be created and normal operation will occur. No 
complicated moving parts are required and the carburetor is not affected 
by this type of speed limiting feature. 
In accordance with the preferred embodiment of the invention, resistor 302 
is variable. Thus, the charging circuit can be varied between curves 
r.sub.1 and r.sub.2, as shown in FIG. 9. Thus, the maximum speed is 
controlled by adjusting resistor 302. In FIG. 9, the firing time after 
capacitor 200 is being charged is identified as t.sub.F. The sparking 
voltage level is indicated by the horizontal line V.sub.F. At time t.sub.F 
a spark would not be created if resistor 302 were set to its maximum level 
and capacitor 200 is charged along line r.sub.2. However, if resistor 302 
were set to its minimum level, capacitor 200 is charged along line r.sub.1 
and sufficient voltage and energy would be available at time t.sub.F. In 
view of the showings in FIGS. 7 and 9, it is apparent that adjustment of 
resistor or rheostat 302 can change the maximum rotational speed of the 
internal combustion engine. As shown in FIG. 8, Zener diode 304 may be 
provided so that the value of the charging voltage E is maintained 
constant. This is optional and is used as a control feature.