Turbocharging, function

General function requirements

 Circuit 61 ON

Charging, general

Charging serves to make an appropriate boost pressure available to the engine in every operating phase and thus to increase engine performance and engine torque. For exhaust gas turbocharging, the flow energy of the exhaust gases is used to drive the turbocharger. The turbocharger draws in fresh air at the compressor intake, compresses it and directs it through the compressor outlet, the charge air pipe, the charge air cooler and the air intake manifold to the engine's individual cylinders.

Turbocharging is regulated by the boost pressure control.

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The boost pressure is regulated by the CDI control unit (N3/9) depending on the following values and associated components:

- Boost pressure, through the boost pressure sensor (B5/1)

- Coolant temperature, through the coolant temperature sensor (B11/4)

- Charge air temperature, through the charge air temperature sensor (B17/8)

- Atmospheric pressure, through the pressure sensor downstream of air filter (B28/5)

- Exhaust temperature upstream of turbocharger, through the temperature sensor upstream of turbocharger (B19/11), for vehicles with code (474) particulate filter

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- Injection quantity, through the injection time of the fuel injectors (Y76) and fuel pressure in the rail

- Fuel pressure in the rail, through the rail pressure sensor (B4/6)

- Exhaust back pressure in the exhaust system, through the exhaust back pressure sensor (B60)

- Engine speed, through the crankshaft position sensor (L5)

Function sequence

After evaluating the input signals, the CDI control unit actuates RH boost pressure positioner (Y100/1) with a PWM signal, according to the boost pressure performance map. The position of the guide vanes in the turbocharger is determined by the control rods of the right boost pressure positioner. 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 monitored continuously by the boost pressure sensor, and the signal is sent to the CDI control unit.

To protect the turbocharger from thermal and mechanical overload, the CDI control unit monitors the exhaust temperature through the temperature sensor upstream of the turbocharger (on vehicles with code (474) particulate filter) and the exhaust back pressure through the exhaust back pressure sensor.

The boost pressure is reduced if there is a risk of thermal or the mechanical overload.

 The charge air heated by the charging is cooled in the charge air cooler.