Download Ignition system lecture

Small Engines
Ignition System
Ignition System Function
• Ignite the fuel and air mixture at the proper
time.
• Advance and retard the ignition timing as
needed.
• “Ground-out” the ignition system so the
engine will stop running.
Ignition Parts Battery type
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Battery
Ignition coil
Ignition switch
Low voltage wires (battery volts)
Ignition Pick-up ( points or electronic)
High Voltage wire(s)
Spark Plug
Ignition Principles
• Electromagnetic Induction
• How does the Ignition Coil work?
• Primary winding: creates a magnetic field
by running current through it.
• When we open the circuit current stops, and
the electromagnetic field collapses.
Ignition Coil Parts
• Primary Winding
• Secondary Winding
• Iron Core
Switching current in Primary
• Breaker Points and condenser
• Points: Mechanical switch
• Condenser: makes the switch last longer so
the points don’t “ burn out”
Self Induction
• When you run current through a coil of
wire, you create a magnetic field. When you
“open” the current flow through that coil of
wire you collapse that magnetic field into
itself.
Coil output
• You produce about 1 volt per turn of wire
• Example: 225 turns of coil wire can
produce up to 225 volts, however your
current output drops at the same rate that
you voltage increases.
Induction Principle
Coil of wire + Current flow = Magnetic field
Magnetic field + Coil of wire = Current flow
*Remember you must have the magnetic field
or the coil of wire moving to have induction
Mutual Induction
• When you have two coils of wire in one
housing.
• You create a magnetic field with one coil
(primary)
• You collapse the magnetic field into both
coils Primary and Secondary
Mutual Induction Output
• You can increase or decrease voltage output
of your induction coils, by changing the
primary and secondary windings ratio.
• Example: primary 250 turns
•
secondary 20,000 turns
• Secondary output could reach up to 20,000
volts!! This is called a Step-up transformer
Continued
• 250 turns primary and 20 turns secondary.
• Maximum output 20 volts.
• This is a “step-down” transformer.
“Magnetron Ignition”
Magnetron Coil
• The magnetron coil actually
contains 3 separate coils of
windings. In addition to the
primary and secondary windings,
there is a 3rd winding, called the
"trigger coil”.
Magneto Ignition
Building the magnetic field
• ." When the leading edge of the
magnets in the flywheel approach the
coil, the magnetic field surrounding
those magnets generates a small
voltage (about 1 volt) that powers a
solid-state switching device called a
Darlington Transistor, turning the
transistor "on." That "on" mode
completes the circuit on the primary
winding and a current of about 3 amps
flows to ground on the crankcase
Collapsing the magnetic field
• As the flywheel continues to rotate that
current builds the magnetic field around
the secondary winding.When the trailing
edge of the magnets the flywheel
reaches the trigger coil, a second small
current is induced in the trigger coil and
that current tells the transistor to "turn
off", effectively breaking the circuit of
the primary winding to ground (Figure
3), the sudden break causes the
magnetic field to collapse.
• Since current (amperage) and voltage
are inversely proportional, suddenly
stopping the current flow causes the
voltage to "spike" as it compensates. It's
that spike that builds the voltage
required in the secondary winding to
jump the sparkplug gap and ignite the
mixture. By the way, in the Magnetron
coil, the primary winding has 74 turns of
wire and the secondary has 4400. That's
a 59.5:1 ratio and that helps insure that
there's enough voltage to get the job
done.
• All this, the initial current in the trigger
coil, the buildup of potential, the second
trigger coil pulse, and the collapsing field
with the resulting voltage spike and
spark, in on about 10 degrees of crank
rotation. That means that at 6000 RPM
the whole thing, start to finish, only takes
about 0.00027 seconds. Pretty amazing.
This simple, but very effective, spark
control system even advances the
ignition timing, causing the plug to fire
earlier (in degrees of crank rotation) as
RPMs go up.