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POWER ENERGY AND
TRANSPORTANTION
THE IGNITION SYSTEM
Mr. Van de Car
THE IGNITION SYSTEM
OVERVIEW
The primary
purpose of the
ignition system
of a small
gasoline engine
is to provide
enough electrical
voltage to
discharge a
spark between
the electrodes of
the spark plug.
THE IGNITION SYSTEM
OVERVIEW
The spark must
occur at exactly
the right time to
ignite the highly
compressed airfuel mixture in
the combustion
chamber of the
engine.
THE IGNITION SYSTEM
•
Electricity can be produced in three
ways:



•
Mechanically
Chemically
Statically
Electricity used in homes and factories
is produced mechanically. Batteries are
chemical producers of electricity.
Lightning is a result of static electricity.
MAGNETS AND ELECTRICITY
The fact that
there is a close
relationship
between
electricity and
magnetism
serves as the
basis for making
a workable
magneto.
MAGNETS AND ELECTRICITY
If a wire is
moved past a
magnet, the
magnetic is
cut by the
wire an
current will
flow.
MAGNETS AND ELECTRICITY
When
movement of
the wire is
stopped, the
current also
stops.
THE MAGNETO
A conductor passing
through a magnetic field
creates an electrical
charge
THE MAGNETO


Magneto supply the
ignition spark on most
small engines.
A magneto will
produce current for
ignition without any
outside primary
source of electricity.
THE MAGNETO
•
•
The coil, condenser, breaker points
and spark plugs make up the primary
and secondary circuits of the
magneto.
Magnets create current flow in
primary winding of coil, which
induces current in secondary winding.
THE MAGNETO



Magnets are usually
cast into the
flywheel and cannot
be removed.
They are strong,
permanent magnets
that are made of
“Alnico” –
aluminum, nickel
and cobalt alloy.
May also be made of
a newer ceramic
magnetic material.
PRIMARY and SECONDARY
WINDINGS





The coil is cut away to
show primary and
secondary windings.
The primary winding
usually has about 150
turns of relatively heavy
copper wire.
The secondary winding has
approximately 20,000
turns of very fine copper.
One end of the primary
and one end of the
secondary is grounded to
the soft iron laminated
core.
The core is then grounded
to the engine.
MAGENTO CORE


The core has an odd
shape designed to
efficiently direct the
magnetic lines of force.
The spacing between
the magnets and the
core ends is critical and
can greatly affect the
whole system
MAGNETO CORE


The breaker points
are mechanically
actuated, opened by
the cam and closed
by the breaker point
spring.
The breaker point
gap is adjusted by
loosening the screw
A and turning
eccentric screw B to
move the stationary
point
A
B
MAGNETO CYCLE

As the flywheel turns,
the magnets pass the
legs of the laminated
core of the coil.

When the north pole of
the magnet is over the
center leg of the
lamination, the
magnetic lines of force
move down the center
leg through the coil,
across the bottom of
the lamination and up
the side leg to the
south pole.
MAGNETO CYCLE

As the flywheel continues
to turn, the north pole of
the magnet comes over
the side leg and the south
pole is over the center leg
of the lamination.

Now the lines of force
move from the north pole
down through the side leg
and up through the center
leg and the coil to the
south pole.

At this point the lines of
force have reversed
direction.
MAGNETO CYCLE



Field reversal taking
place in the center leg
of the lamination and
the coil.
The reversal creates
low voltage current in
the primary circuit
through the breaker
points.
Magnetic field
reversal takes place
as magnets pass
from left to right.
Breaker points are
closed.
MAGNETO CYCLE




Current flowing in the
primary windings of the
coil creates a primary
magnetic field of its own.
This reinforces and helps
maintain the direction of
the lines of force in the
center leg of the
lamination.
This continues until the
magnetic poles move into
a position where they can
force the existing lines of
force to change direction
in the center leg of the
lamination.
Just before this happened
the breaker points are
opened by the cam.
MAGNETO CYCLE




Opening of the points
breaks the primary
circuit
The primary magnetic
field collapses through
the turns of the
secondary windings.
The condenser makes the
breaking of the primary
current as instantaneous
as possible by absorbing
the surge of primary
current.
This prevents arcing
between the breaker
points.
MAGNETO CYCLE
•
Breaker points open and
the primary magnetic field
collapses at an extremely
high rate through
secondary windings
•
This causes the high
voltage needed to fire the
spark plug.
•
The field collapse also cuts
through windings of the
primary coil which causes
moderate voltage that is
absorbed by the
condenser.
MAGNETO CYCLE




This change in direction
sets up a reversal in
direction of magnetic
field cutting through the
secondary.
This helps increase the
voltage in the secondary
circuit.
The potential of the high
voltage causes secondary
current to arc across the
spark plug gap.
Spark plug fires and
condenser discharges
voltage back into primary
circuit.