Turbocharging, function

General function requirements

 Circuit 61 ON

Charging, general

Forced induction is used to provide the engine with the appropriate boost pressure in all operating phases, thus increasing engine power and torque. In 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:

- Left intake air temperature sensor (B2/6b1)

- Right intake air temperature sensor (B2/7b1)

- Boost pressure sensor (B5/1)

- Coolant temperature sensor (B11/4)

- Charge air temperature sensor (B17/8)

- Pressure sensor downstream of air filter (B28/5), for the atmospheric pressure

- Temperature sensor upstream of turbocharger (B19/11)

- The injection quantity which is determined via the injection time of fuel injectors (Y76) and the fuel pressure in the rail. The fuel pressure in the rail is detected by the rail pressure sensor (B4/6).

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

- Crankshaft Hall sensor (B70), for engine speed

Function sequence

After evaluating the input signals, the CDI control unit actuates the boost pressure positioner (Y77/1) with a PWM (pulse width modulated) signal, according to the boost pressure map. The position of the guide vanes in the turbocharger are altered via the control linkage on the boost pressure actuator. 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 (B5/1) 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 through 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 a risk of thermal or the mechanical overload.

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