Functional Description of EGM
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Status September 2003 (EvoBus-Service / AFT) Page: 31 of 83
2.4.3 Turbocharger control
The M 447 hLAG is equipped with a water-cooled rigid-geometry turbocharger. Output control is realised
with a wastegate. The wastegate is actuated by a pneumatic actuator. If the pneumatic actuator is not
charged with pressure, then the wastegate is closed.
Schematic diagram of wastegate actuation
The operating pressure of the pneumatic actuator is controlled by an electropneumatic converter (EPW).
The EGM carries out a boost-pressure control and actuates the EPW with a PWM of 120 Hz and a variable
pulse duty factor. The boost-pressure control is calculated in a 20 ms time grid.
The EPW for actuating the boost pressure is not actuated in the engine states "Engine stopped" and
"Starting". In the "Normal operation" engine state the target boost pressure is a function of the requested
vehicle torque and the engine speed.
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