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8.5
Section 8
Electrical System and Components
8
Figure 8-4. Capacitive Discharge (Fixed Timing) Ignition System.
Kill Switch or
‘‘Off’’ Position of
Key Switch
Ignition
Modules
Spark Plug
Magnet
Flywheel
(0.28/0.33 mm)
0.011/0.013 in. Air Gap
L1
D1
C1
T1
P
S
Spark Plug
L2
SCS
Figure 8-5. Capacitive Discharge Ignition Module Schematic.
The timing of the spark is controlled by the location of the flywheel magnet group as referenced to engine top dead
center.
B. Capacitive Discharge with Electronic Spark
Advance (SMART-SPARK
™
).
SMART-SPARK
™
equipped engines utilize an
electronic capacitive discharge ignition system with
electronic spark advance. A typical application (Figure
8-6) consists of the following components:
• A magnet assembly which is permanently affixed
to the flywheel.
• Two electronic capacitive discharge ignition
modules which mount on the engine crankcase
(Figure 8-6).
• A spark advance module which mounts to the
engine shrouding (Figure 8-7).
• A 12 volt battery which supplies current to the
spark advance module.
• A kill switch (or key switch) which grounds the
spark advance module to stop the engine.
• Two spark plugs.
Operation: As the flywheel rotates, the magnet
grouping passes the input coil (L1). The corresponding
magnetic field induces energy into the input coil (L1).
The resultant pulse is rectified by D1 and charges
capacitor C1. As the magnet assembly completes its
pass, it activates the triggering device (L2), which
causes the semiconductor switch (SCS) to turn on.
With the device switch “ON,” the charging capacitor
(C1) is directly connected across the primary (P) of the
output transformer (T1). As the capacitor discharges,
the current initiates a fast rising flux field in the
transformer core. A high voltage pulse is generated
from this action into the secondary winding of the
transformer. This pulse is delivered to the spark plug
gap. Ionization of the gap occurs, resulting in an arc at
the plug electrodes. This spark ignites the fuel-air
mixture in the combustion chamber.