6.
MAGNETO
0
6-1
FLYWHEEL
MAGNETO
".
The ignition system of the
EH18V
is a pointless flywheel magneto .with an autcmatic advancing
characteristic.
Being different from the breaker point type ignition system, this- system
is
completely free from such
troubles as starting-up failure due to dirty, burnt or corroded point surface. The electronic automatic
advancing ensures extremely easy starts and stable high performance at operating speed
by
advancing the
ignition timing to the most suitable point.
6-2
BASIC
THEORY
.
To
ensure the easy startability of the engine, the step advancing ignition timing system
is
incorporated in
the ignition coil. This system enables the engine to have basically two different ignition timings
according
to
the engine speed. Following are the explanation how the system works.
1)At lower speed of the engine
Rotation of the flywheel induces current
I,,
as this current flows through the base terminal
of
the power
transistor, it
is
activated and the current
LZ
starts flowing.
As
the engine reaches the ignition timing, the ignition timing control circuit
for
the lower engine speed
is
activated and lets the current
b
flow through
the
base terminal of the power transistor.
This generates the collector current
L
which will bypass the current
11
and abruptly shut off the current
IZ
because the power transistor is turned off.
This sudden current change generates a big voltage on the secondary side
of
the ignition coil and which
sparks the spark plug.
Rotation of the flywheel generates the current
11
as this current flows through the base terminal
of
the
power transistor, it is activated and the current
12
starts flowing.
As
the
engine reaches the ignition timing, the ignition timing control circuit for the higher engine
speed
is
activated and provides the base current
Is
to the power transistor. This current induces the
collector current
16
and will bypass the current
IL
to shut down
the
current
IZ
abruptly because the power
transistor
is
turned
off.
This sudden current change generates
a
big voltage
on
the secondary side of the ignition coil causing
sparks
at
the spark plug.
The ignition timing control circuit for the higher engine speed is activated sooner than the control
circuit for the lower speed and not activated when the engine speed is in a lower range.
2)At the higher engine speed
-41
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