Forced induction, function

Function requirements for charging - general

 Circuit 87M ON (engine control ON)

 Circuit 61 ON

Forced induction, general

The cylinder charging efficiency is improved as a result of forced induction. As a result, the engine torque and power output are boosted. During forced induction, 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 turbine wheel 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.

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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 (N3/28) depending on the following values and associated components:

- Boost pressure sensor (B5/6)

- Coolant temperature sensor (B11/17)

- Charge air temperature sensor (B17/13)

- Intake manifold pressure sensor (B28/17)

- Temperature sensor upstream of diesel particulate filter (B19/17)

- Exhaust back pressure sensor (B60/3), for the exhaust back pressure in the exhaust system

- Temperature sensor upstream of turbocharger (B16/13)

- Crankshaft sensor (L5/10), for the engine rpm

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- Injection quantity which is detected by the rail pressure sensor (B4/16) is determined by the fuel pressure in the rail and the injection time of the following injectors:

- Cylinder 1 injector (Y76/14)

- Cylinder 2 injector (Y76/15)

- Cylinder 3 injector (Y76/16)

- Cylinder 4 injector (Y76/17)

- Atmospheric pressure sensor (integrated in the CDI control unit), for detection of the atmospheric pressure

Function sequence for charging

After evaluating the input signals, the CDI control unit actuates depending on the charge pressure performance map of the boost pressure actuator (Y77/6) by means of a pulse width modulation (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.