39
The flywheel
21. 40 holes are machined in the circumference of
the flywheel. The space between the holes act as
teeth thus the flywheel can be regarded as a toothed
wheel.
Since a 4 cylinder 4 stroke engine needs 2 sparks
per revolution, the toothed wheel is divided into two
halves. Each half has 20 teeth. Of these, 2 teeth in
each half turn are double the others in size. These
two big teeth are the reference points for the location
of the upper and lower ‘dead centers’. The points of
reference are located 90° before the upper and lower
‘dead centers’ respectively.
Signal Processing
22. The crankshaft position sender sends a signal
each time a tooth passes by. It also provides the
control unit with information when each of the 2 big
teeth pass by. Thus the position of the upper ‘dead
center’ is known since it is positioned 11 teeth after
the long tooth.
The function
23. Half a turn before each explosion cycle the con-
trol unit is calculating a very exact pre-ignition going
out from the speed of the engine. There are 63 op-
timized engine speed values stored in the control
unit’s non-volatile memory. From these the control
unit selects a suitable ignition time.
Speed Control
24. In order not to damage the engine by over rev-
ving it there is an electronic function available which
reduces the dwell angle (the charging time of the ig-
nition coil) at 103.33 r/s (6200 rpm). The system
provides ignition but the output of the engine is so
low that it cannot increase the engine speed.
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