Charging, function

Function requirements, general

 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 unit and leads it pre-compressed to the individual cylinders via the compressor outlet, the charge air pipe, the charge air cooler and charge air manifold.

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)

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

- 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 in exhaust system via exhaust back pressure sensor (B60) on vehicles with code (474) Particulate filter

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

 The charge air compacted and warmed by the charging is cooled in the charge air cooler.

Function sequence up to ÄJ10 or with code (U41) Fuel/water separator and lubricating package

For engine 640.940/942 the CDI control unit actuates the boost pressure control pressure transducer (Y31/5) by means of pulse width modulated (PWM) signal dependent on the boost pressure performance map after evaluation of the input signals. The boost pressure control flap is adjusted over the boost pressure control vacuum unit and a linkage. Depending on the flap position, part of the exhaust flows through a bypass on the turbocharger thereby controlling the boost pressure.

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On engine 640.941, after evaluating the input signals, the CDI control unit actuates depending on the charge pressure performance map of the boost pressure transducer by means of a pulse PWM signal. The guide vanes in the exhaust turbocharger are adjusted by the boost pressure vacuum unit and linkage thereby regulating the boost pressure.

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

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

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Function sequence J10 except code (U41) Fuel/water separator and lubrication package and with code (928) exhaust treatment with EU5 technology

After evaluating the input signals, the CDI control unit actuates depending on the charge pressure performance map of the boost pressure actuator (Y100/2) by means of a pulse 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 monitored by the charge pressure sensor and passed on to the CDI control unit.

The exhaust back pressure is monitored by the exhaust back pressure sensor by the CDI control unit as protection against thermal and mechanical overload of the turbocharger.

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