Page 255 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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Engine systems 239

Figure 2.316 First Bosch high-voltage magneto ignition system with spark plug in 1902.
(Source: Bosch Media)

Table 2.3 Traditional ignition components

Component Function
Spark plug Seals electrodes for the spark to jump across in the cylinder. Must
withstand very high voltages, pressures and temperatures

Ignition coil Stores energy in the form of magnetism and delivers it to the
distributor via the high-tension (HT) lead. Consists of primary and
secondary windings
Ignition switch Provides driver control of the ignition system and is usually also
used to cause the starter to crank
Contact Switches the primary ignition circuit on and off to charge and
breakers discharge the coil. The contacts are operated by a rotating cam in
(breaker points) the distributor
Capacitor Suppresses most of the arcing as the contact breakers open.
(condenser) This allows for a more rapid break of primary current and hence a

more rapid collapse of coil magnetism, which produces a higher
voltage output

Distributor Directs the spark from the coil to each cylinder in a preset sequence
Plug leads Thickly insulated wires to connect the spark from the distributor to
the plugs

Centrifugal Changes the ignition timing with engine speed. As speed
advance increases the timing is advanced
Vacuum Changes timing depending on engine load. On conventional
advance systems the vacuum advance is most important during cruise
conditions

Energy storage takes place in the ignition coil. The energy is stored in the form of
a magnetic fi eld. To ensure the coil is charged before the ignition point, a dwell
period is required. Ignition timing is at the end of the dwell period as the coil is
switched off.

2.6.1.4 Traditional ignition system

Very early cars used something called a magneto, which is a story for another
time, but Fig. 2.316 shows a nice picture of one anyway! For many years
ignition systems were mechanically switched and distributed. Table 2.3 gives an
overview of the components of this earlier system (see Figs 2.317–2.320 ).