3 ignition system – Subaru Robin EX30 User Manual
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7-3 IGNITION SYSTEM
7-3-1 IGNITION COIL INTERNAL CIRCUIT
7-3-2 IGNITION TIMING CHARACTERISTIC
7-3-3 BASIC THEORY
(a) Revolution of the fl ywheel generates electricity on the primary side of the ignition coil ( ① ), and the base
current I
1
fl ows to the power transistor (
). Current I
1
turns the power transistor "ON" and the electric current
I
2
fl ows. This is the same situation when the contact breaker is closed in a case of breaker point type ignition
system.
(b) At lower engine revolution, the low speed ignition timing control circuit (
) operates to run the gate current
I
3
to turn the control thyristor (
) "ON" thus the current I
1
bypass the thyristor as current I
5
.
At this moment, the power transistor (
) turns "OFF" and the current I
2
is shut off abruptly resulting in the
high voltage generated in the secondary coil (
) which produces sparks at the spark plug.
The ignition timing at lower engine revolution is less advanced as shown in the above chart.
(c) At higher engine revolution (over 2,000rpm), advancing control circuit (
) operates to run the gate current I
4
to turn the control thyristor (
) "ON" , thus the current I
1
bypass the thyristor as current I
5
.
At this moment, the power transistor (
) turns "OFF" and the current I
2
is shut off abruptly resulting in the
high voltage generated in the secondary coil (
) which produces sparks at the spark plug.
At over 2,000rpm, ignition timing on each engine revolution is controlled by advancing control circuit (
) that
receive electrical information from revolution sensing resister (
).
The advancing of ignition timing from lower to higher engine revolution changes lineally as shown in the above
chart.
3
4
5
2
6
1
7
I
3
I
4
I
1
I
2
Low Speed Ignition
Timing Control
Circuit
Base Resister
Advancing Control
Circuit
Control thyristor
I
5
Revolution Sensing Resister
Power T
ransistor
Primary Coil
Spark Plug
Secondary Coil
0
0
500
1000
1500
2000
2500
3000
3500
4000
5
10
15
20
25
30
35
IGNITION TIMING
B.T
.D.C.( )
LINEAR ADVANCING
ENGINE REVOLUTION (R.P.M.)