8.6
Section 8
Electrical System and Components
Electronic Ignition System with Spark Advance (Smart Spark
™
), CH16 Engines
Figure 8-5. Capacitive Discharge Ignition System with Spark Advance.
CH16 engines are equipped with an electronic
capacitive discharge ignition system with electronic
spark advance. A typical application (Figures 8-5 and
8-6) consists of the following components.
• A magnet assembly which is permanently
affixed to the flywheel.
• An electronic, capacitive discharge ignition
module which mounts on the engine crankcase.
• A spark advance module which mounts to the
engine shrouding.
• 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.
• A spark plug.
Figure 8-6. Smart Spark
™
Components.
Operation
As the flywheel rotates, the magnet grouping passes
the input coil (L1) of the ignition module, inducing
energy in the coil. The resultant pulse is rectified by
diode (D1) and charges capacitor (C1). Current from
the same pulse also travels through the brown lead to
the spark advance module (SAM), and enters the
input of the conditioning circuit. The conditioning
circuit shapes this pulse, putting it in a useable form
for the other circuits. The
conditioned
pulse starts the
charge pump, which charges a capacitor in linear
fashion, directly related to engine speed. The pulse
also resets the delay circuit. The comparator is off
during this period.
When the flywheel magnet group has passed the
input coil, and the original pulse drops back to zero,
the capacitor in the delay circuit begins to charge off
of the power source. When the charge on the delay
capacitor exceeds the charge pump capacitor, the
comparator changes state and activates the pulse
generator, The
generated
pulse returns to the ignition
module through the yellow lead and turns
on
the
semiconductor switch (SCS), completing the circuits
between the charging capacitor (C1) and the
transformer (T1). The charging capacitor discharges
into the transformer primary (P), inducing a high-
voltage pulse in the transformer secondary (S). The
high-voltage pulse arcs across the spark plug gap,
igniting the fuel-air mixture in the combustion
chamber. The longer it takes the delay circuit to
surpass the reference voltage in the charge pump
capacitor, the later the trigger pulse will occur,
retarding the timing accordingly.
Kill Switch or Off
Position of Key Switch
Air Gap
(0.2/0.3 mm)
0.008/0.012 in.
Flywheel
Magnet
Ignition Module
Spark Plug
12 Volt Battery
Spark Advance Module
