Flywheel magneto generator

A magneto generator for an engine having a flywheel, in which the flywheel comprises a rotor mounted for axial rotation and has a rim of magnetically permeable material. A magnetically permeable core has first and second ends located adjacent to the rim at circumferentially spaced points. At least two wire coils are wrapped on the core. The rim defines a permeability path between the ends of the core. A fixed magnet is placed on one end of the core. The rim is interrupted at circumferentially spaced points to provide walls and windows alternately making and breaking the permeability path when the rotor is rotated to produce voltage pulses in sinusoidal form in the coils. The positive half cycles in one of the coils is used to charge an ignition storage capacitor for energizing a spark plug. The negative half cycles in the other winding are used to charge a battery.

FIELD OF INVENTION 
This invention relates generally to magnetos and more particularly to a 
magneto for the ignition system of an engine. 
BACKGROUND OF THE INVENTION 
Typically, small two and four-stroke engines are equipped with flywheels 
and magneto ignitions. A magnet is mounted on the flywheel and the flux of 
the magnet is brought out to the working radius of the flywheel by pole 
shoes made of magnetically conductive material. In these systems, the 
ignition module is mounted as a stator assembly in fixed position and 
comprises a U-shaped core of magnetically conductive material, the ends of 
which are positioned close to the path of the pole shoes on the flywheel. 
The magnet on the rotating flywheel produces a magnetic field through the 
permeability path provided by the stator core. One or more coils are 
wrapped on the core and when the flux passes through the core, a voltage 
is generated in the coils. This generated voltage may be stored in a 
capacitor and stepped up by a transformer to the potential needed for 
ignition of the air/fuel mixture of the engine. 
One disadvantage of this system is that the flux is generated in the core 
only once for each revolution of the flywheel. This represents 
approximately 15.degree.-20.degree. in the full 360.degree. of one 
revolution of flywheel rotation. The system is electrically down during 
the balance of the cycle. Another disadvantage is in the manufacturing 
process which usually requires the magnet and an offsetting counterweight 
to be insert die cast into the flywheel. This causes uneven cooling of the 
casting, represents additional time and labor costs, and adversely affects 
the strength and structural integrity of the flywheel. 
In a more recent development, the magnet, rather than being mounted on the 
flywheel, has been mounted on a core in a fixed position. 
SUMMARY OF THE INVENTION 
The present invention is an improvement on the more recent development 
described above. In accordance with this invention, the magnet is mounted 
on a core in a stationary module located closely adjacent to the flywheel. 
The flywheel has alternate walls and windows or gaps to open and close the 
permeability path during rotation of the flywheel. Voltage pulses in 
sinusoidal waveform are generated in a charge circuit on the core for each 
revolution of the flywheel. 
The charge circuit is preferably composed of two coils and two diodes. 
During the positive half of the sine wave pulses, one of the coils 
produces the voltage needed to charge the ignition storage capacitor. 
During the negative half of the pulses, the other coil charges a battery. 
The battery provides a source of energy for other devices such as electric 
starter motors, solenoids, microprocessors, and stepper motors. 
One object of this invention is to provide a magneto generator for an 
engine having the foregoing features and capabilities. 
Another object is to provide a magneto generator which is composed of a 
relatively few simple parts, is rugged and durable in operation, and is 
simple and inexpensive to manufacture and assemble.

DETAILED DESCRIPTION 
Referring now more particularly to the drawings, and especially to FIGS. 1 
to 4 thereof, the engine 20 is a small two or four-stroke engine of the 
type used to drive a lawn mower or snowblower, for example. The engine has 
a flywheel 22 with a rotor 24 which is mounted on the engine for axial 
rotation. More specifically, the flywheel 22 and rotor 24 are secured by a 
bolt 25 to the top of a vertical crankshaft 26 that is operatively 
connected by a rod to a piston (not shown) of the engine. 
As shown in FIG. 2, the engine 20 has a flywheel magneto generator 27 
embodying this invention which includes the rotor 24, a stator module 28 
having a core 34 with coils 36, 38, 40, 42 and 44 wrapped thereon, and a 
permanent magnet 45. The coils 42 and 44 are the primary and secondary of 
an exciter 46 for the spark plug SP. 
The rotor 24 comprises a generally circular reluctor wheel 47 preferably 
formed of a laminated stack of discs made of a highly magnetically 
permeable material such, for example, as steel or a powdered metal mixture 
of iron and phosphorous. The rotor 24 also has a generally circular plate 
48 of steel, for example, secured to the top surface of the body 49 of the 
wheel 47. The plate 48 is shaped to form vanes 50 bent to produce a flow 
of cooling air to the engine when the rotor rotates. 
The wheel 46 has an integral cylindrical rim 52 which is perpendicular to 
the body 49 thereof. The rim 52 is notched to provide a plurality of 
equally, circumferentially spaced and axially extending walls or tabs 56. 
The tabs 56 are arranged in a circle forming segments of a cylinder 
concentric with the rotational axis of the rotor and perpendicular to the 
body 49 of the wheel, with spaces or gaps 60 forming windows between 
adjacent tabs. 
The core 34 of the stator module 28 is generally U-shaped and is mounted in 
fixed position on a wall 66 of the engine body, at one side of the rotor 
24. The core has a first end 68 and a second end 70 which are close to the 
circle of tabs 56. The core 34 is made of a highly magnetically permeable 
material such as a plurality of laminated plates of steel. The wire coils 
36-44, each comprising a plurality of turns of an electrically conductive 
wire such as copper, are wrapped around the core. The magnet 45 is mounted 
on the first end 68 of the core between the core and the rotor. The magnet 
is made of any suitable magnetic material such, for example, as neodymium 
and is generally rectangular in form, preferably having the dimensions 
9.times.9.times.5 millimeters. The space between the magnet 45 and the 
circle of the outer faces of the tabs 56 and likewise the space between 
the second end 70 of the core 34 and the circle of the outer faces of the 
tabs is on the order of about 0.3 millimeters to form a very small air 
gap. 
The arcuate distance between the magnet 45 and the second end 70 of the 
core 34 is substantially the same as the arcuate distance between adjacent 
tabs 56, so that when one tab is opposite the magnet, the next adjacent 
tab is opposite the second core end 70, at which time the permeability 
path from one core end 68 to the other core end 70 passes through the 
rotor wheel 47, as shown by the broken line 76 in FIG. 2. The magnet 45 is 
in the permeability path. When a space 60 between tabs is opposite the 
magnet 45, the next adjacent space 60 is opposite the second end 70 of the 
core, thus breaking the permeability path so that the magnetic flux in the 
core 34 collapses. Thus, when the rotor is rotating, the tabs 56 and 
spaces 60 provide walls and windows or gaps alternately making and 
breaking the permeability path, producing an alternating sinusoidal wave 
form and voltage pulses in the coils 36-44. The sine wave is continuous 
and repeats during the rotation of the flywheel. The same wave form will 
be produced in all of the coils 36-44. 
Rather than making the spacing between the ends of the core equal to the 
spacing between adjacent tabs, the spacing between the core ends could be 
any multiple of the spacing between adjacent tabs. 
A cover plate 77 is secured to the engine body and encloses the rotor 24, 
the core 34, coils 36-44 and the magnet 45. Air is admitted through 
openings 78 in the cover plate 77. 
In use during operation of the engine 20, the tabs 56 and spaces 60 of the 
rotor 24 rapidly make and break the permeability path several times during 
each revolution of the flywheel rotor 24, producing voltage pulses in the 
coils 36-44. The permeability path extends from tab to tab across the 
unnotched portion of the rotor between tabs during the full 360.degree. of 
rotor rotation. 
Referring to FIG. 6, the coil 36 is the ignition charge coil which is 
connected to a capacitor 80 through a diode 82 which half-wave rectifies 
the current output so that the capacitor is charged with the positive half 
cycles only of the alternating current. The ignition charge coil 36 
preferably has a large number of turns, for example 2500, of fine wire to 
generate the approximately 300 volts necessary for charging the capacitor. 
The coil 38 is the battery charge coil which is connected to a battery 84 
through a diode 86 which half-wave rectifies the current output so that 
the battery is charged with the negative half cycles only of the 
alternating current. The battery charge coil 38 preferably has fewer 
turns, for example 25-50, of a larger diameter wire to produce a series of 
pulses of approximately 12 volts to charge the battery. The battery thus 
provides a constant source of energy that can be used for electric starter 
motors, solenoids, microprocessors, stepper motors and other devices. 
The coil 40 is the trigger coil which responds to a single magnetic pulse 
for each revolution of the flywheel. This may be accomplished by a sensor 
mounted near the periphery of the flywheel with an appropriate marking on 
the flywheel which the sensor detects. This may also be accomplished as 
shown in FIG. 7, where one tab 89 of the flywheel rotor has a plain 
stamped steel leg 90. The trigger coil may be mounted on a fixed 
structural element 92 very close to the circular path of the leg 90. The 
magnetic flux passes from the magnet 45 across the air gap to the tab 89, 
along the leg 90 and across the air gap to the trigger coil 40, and then 
by the air path to the core 34. This will produce a pulse in the coil 40 
for each 360.degree. of flywheel rotation sufficient to trigger the 
capacitor at the proper time to energize the primary coil 42 of the 
exciter 46 for the spark plug SP. The second coil 44 of the exciter 
produces a sufficiently high voltage to produce the spark.