Subaru EX13 Service Manual page 52

7-3 IGNITION SYSTEM (EX13 ,17, 21)
7-3-1 TYPE OF IGNITION SYSTEM
EX13, 17 and EX21 have the T.I.C. (Transister, Igniter, Circuit) pointless ignition system.
As optional parts, these ignition system may be implemented with lamp coil, charge coil and excitor coil.
LowSpeed
Ignition
Timing
Control Circuit
7-3-2 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 transister, it is activated and the
current I2 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 I
This generates the collector current I
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.
2) At the higher engine speed
Rotation of the flywheel generates the current I
transistor, it is activated and the current I
As the engine reaches the ignition timing, the ignition timing control circuit for the higher engine speed is
activated and provides the base current I
I and will bypass the current I
6
This sudden current change generates a big voltage on the secondary side of the ignition coil and which will
spark 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.
I
3
Automatic
Advancing
Control
Circuit
I
4
,
1
flow through the base terminal of the power transistor.
3
which will bypass the current I
4
as this current flows through the base terminal of the power
1
starts of flow.
2
to the power transistor. This current induces the collector current
5
to shut down the current I
1
- 49 -
I
1
I
5
I
I
6
Fig. 7-1(a)
ELECTRONIC ADVANCING FLYWHEEL
MAGNETO SYSTEM
(B.T.D.C)
23
STEP ADVANCING
15
500 1000
ENGINE REVOLUTION
Fig. 7-1(b)
and abruptly shut off the current I
1
abruptly because the power transistor is turned off.
2
2
2000 3000(r.p.m.)
2