Man D 2840 LE 301, Repair Manual

Page: 144 / 194

Electronic speed control
142
Basic design
An electronic control system consists of three components:
1. Speed pickup
In MAN engines the speed pickup
Á
, which works according to the induction principle, is located on the
flywheel housing. It consists of a permanent magnet surrounded by a coil.
Depending on whether a tooth of the starter gear ring
À
is before the magnet or not, the magnetic field
changes and induces in the coil an alternating voltage which is proportional to the engine speed and
serves as input signal for the control unit.
1 2
2. Electronic control unit
The electronic control unit receives the signal (actual value) generated by the pickup and compares it
with a preset value (nominal value).
If the actual and the nominal values are identical, the electronic control unit will generate an output
signal with which the final control element will be triggered.
3. Final control element
In GAC governors, for example, the final control element is a spring-loaded linear solenoid.
This solenoid is connected to the control rod of the injection pump and changes its position according to
the signal from the control unit. As a result, the injection quantity and, consequently, engine speed are
controlled.