Robin EH09D, Service Manual, Page: 51 / 84

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(2) At lower engine revolution, when the flywheel reached the ignition point the low speed ignition timing
control circuit operates to run the base current
I
3
to turn the signal transistor A “ON” allowing the
current I
1
to bypass as current I
4
.
At this moment the power transistor turns “OFF” and the current I
2
is abruptly shut off resulting in the
high voltage generated in the secondary coil which produces sparks at the spark plug.
(3) At higher engine revolution, the advancing control circuit operates at the ignition timing to run the
base current I
5
to turn the signal transistor B “ON” allowing the current I
1
to bypass as current I
6
.
At this moment the power transistor turns “OFF” and the current
I
2
is abruptly shut off resulting in the
high voltage generated in the secondary coil which produces sparks at the spark plug.
The operating timing of the advancing control circuit advances in accordance with the increase of
engine speed resulting in the advancing of ignition timing as shown in Fig. 6-1(b).
Fig. 6-1b
Fig. 6-1a
Low Speed
Ignition
Timing
Control Circuit
I
3
I
4
Signal Transistor
A
Automatic
Advancing
Control
Circuit
I
5
I
6
Signal Transistor
B
I
1
Resister
I
2
Power Transistor
Secondary Coil
Primary Coil
Spark plug
500 1000 2000 3000 (r.p.m.)
(EH12-2D)
(EH09D)
ENGINE REVOLUTION
IGNITION TIMING
STEP ADVANCING
ELECTRONIC ADVANCING FLYWHEEL
MAGNETO SYSTEM
(B.T.D.C.)
15°
18°
23°