Page 257 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

2
Engine systems 241

Figure 2.320 Traditional system using a distributor

Figure 2.321 Power transistor

All current vehicle ignition systems are electronically switched and most are now
digitally controlled as part of the engine management system. However, there are
many vehicles out there still using conventional electronic ignition, so the next
section will give an overview of these systems.

2.6.2 Electronic ignition
2.6.2.1 Constant dwell
Mechanical ignition systems have some major disadvantages:
Mechanical problems with the contact breakers occur, not least of which is the
●
limited lifetime.
Current fl ow in the primary circuit is limited to about 4 A or damage will occur
●
to the contacts; or at least the lifetime will be seriously reduced.
Legislation requires stringent emission limits, which means that the ignition
●
timing must stay in tune for a long time.
Weaker mixtures require more energy from the spark to ensure successful
●
ignition, even at very high engine speed.
These problems were overcome by using a power transistor ( Fig. 2.321 ) to carry
out the switching function and a pulse generator to provide the timing signal.