Turbocharger: Description and Operation

GF09.00-P-2000OG Charging, Function
- ENGINES 642.8 in MODEL 204.0 /2 /9, 207.3 /4, 212.0 /2, 218

Function requirements for charging - general
- Circuit 87M ON (engine control ON)
- Engine running

Charging, general
The cylinder charging efficiency is improved as a result of charging. As a result, the engine torque and power output are boosted. When charging, the flow energy of the exhaust gases is used to drive the turbocharger. The turbocharger suctions in fresh air through the air filter on the compressor inlet and feeds it through the compressor outlet into the charge air pipe upstream of the charge air cooler. The high speed of the compressor impeller and the resultant high volume flow compresses the air in the charge air pipe.

Compression heats the charge air, which now flows through the charge air pipe to the charge air cooler. This cools off the charge air and feeds it through the charge air pipe to the charge air manifold. Turbocharging is regulated by the boost pressure control.

The boost pressure is regulated by the CDI control unit (N3/9) depending on the following values and associated components:
- Boost pressure sensor (B5/1)
- Coolant temperature sensor (B11/4) (model 204, model 207, model 212), coolant temperature sensor (B11/4) (model 218)
- Charge air temperature sensor (B17/8)
- Pressure sensor downstream of air filter (B28/5)
- Temperature sensor upstream of turbocharger (B19/11)
- The injection quantity, determined by the injection time of fuel injectors (Y76) and the fuel pressure in the rails. The fuel pressure in the rails is detected by the rail pressure sensor (B4/6).
- Exhaust back pressure sensor (B60), for the exhaust back pressure in the exhaust system
- Crankshaft Hall sensor (B70), for engine speed
- Atmospheric pressure sensor, for measuring the atmospheric pressure

Function sequence for charging
After evaluating the input signals, the CDI control unit actuates, based on the charge pressure characteristic map, the boost pressure regulator (Y77/1) by means of a pulse width modulated signal (PWM signal). The position of the guide vanes in the turbocharger are altered via the control linkage of the boost pressure regulator.

The adjustable guide vanes modify the flow cross-section through which the exhaust gas flows to the turbine. The guide vanes thus match the gas pressure present at the turbine to the required boost pressure. The turbocharger speed is used to determine the quantity of compress air and thus the boost pressure.
The boost pressure is constantly being monitored by the boost pressure sensor and passed on to the CDI control unit.
To protect the turbocharger from thermal and mechanical overload, the CDI control unit monitors the exhaust temperature via the temperature sensor upstream of the turbocharger and the exhaust back pressure through the exhaust back pressure sensor. The boost pressure is reduced if there is any risk of thermal or mechanical overload.