Subaru EX13 Service Manual page 53

7-4 IGNITION SYSTEM (EX27)
7-4-1 IGNITION COIL INTERNAL CIRCUIT
3
Low Speed Ignition
Timing Control
Circuit
4
7-4-2 IGNITION TIMING CHARACTERISTIC
7-4-3 BASIC THEORY
(a) Revolution of the flywheel generates electricity on the primary side of the ignition coil ( ① ), and the base
current I flows to the power transistor ( ② ). Current I
1
current I flows. This is the same situation when the contact breaker is closed in a case of breaker point
2
type ignition system.
(b) At lower engine revolution, the low speed ignition timing control circuit ( ③ ) operates to run the gate
current I to turn the control thyristor ( ⑤ ) "ON", thus the current I
3
At this moment, the power transistor ( ② ) turns "OFF" and the current I
in the high voltage generated in the secondary coil ( ⑦ ) 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 ( ④ ) operates to run the gate current
I to turn the control thyristor ( ⑤ ) "ON", thus the current I
4
At this moment, the power transistor (②) turns "OFF" and the current I
in the high voltage generated in the secondary coil ( ⑦ ) which produces sparks at the spark plug.
At over 2,000rpm, ignition timing on each engine revolution is controlled by advancing control circuit ( ④ )
that receive electrical information from revolution sensing resister ( ⑥ ).
The advancing of ignition timing from lower to higher engine revolution changes lineally as shown in
the above chart.
Base Resister
5
I
3
Advancing Control
I
Circuit
4
LINEAR ADVANCING
35
30
25
20
15
10
5
0
0 500 1000 1500
I I 2
1 2
6
I
5
Fig.7-2a
2000 2500 3000 3500
ENGINE REVOLUTION (R.P.M.)
Fig.7-2b
turns the power transistor "ON" and the electric
1
bypass the thyristor as current I
1
- 50 -
1 7
4000
bypass the thyristor as current I
1
is shut off abruptly resulting
2
.
5
is shut off abruptly resulting
2
.
5