Spark Plugs
Chapter 3
Study Tips
How is the high voltage produced?
When does the spark discharge occur?
Basics of Ignition
Chapter 3 Basics of Ignition
37
Primary current
and high voltage
The magnitude of the secondary
voltage generated in the ignition coil is
proportional to the magnitude of the
primary current.
However, generally as the figure
shows, the higher the engine speed,
the lower the voltage generated. This
is because the higher the engine
speed, the less time there is for the
primary current to build up and the
value of this current decreases.
Therefore, it is necessary to control the
primary current to be constant from
low speed to high speed. One method
for this control is dwell angle control.
Ignition coil
This generation of high voltage
through such coil self-induction action
and mutual induction action takes
place within the ignition coil.
The ignition coil has two coils, the
primary coil and the secondary coil,
and their winding ratio is about 1:100.
The actual connecting and cutting off
of the primary current is handled by
transistors in the igniter or by
mechanical contacts in the distributor.
Ignition coil circuit
Battery
Ignition switch
Ignition coil
Primary coil
Secondary coil
Signal
Transistor
Spark plug
8
8
7
7
6
6
5
5
4
4
3
3
2
2
1
1
Secondary voltage generation
Ne: Engine speed V: Secondary voltage
Coil A
Coil B
B
B
A
A
1
1
4
4
3
3
2
2
5
5
6
6
8
8
7
7
B
B
A
A
