Charging, function

D09.00-0014-79

Function requirements for charging - general

 Circuit 87M (Engine management ON)

 Engine running.

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 ATL. The ATL suctions in fresh air through the air filter on the compactor inlet and feeds it through the compressor outlet into the charge air pipe upstream of the charge air cooler. The high rpm of the compressor impeller and the resultant high volumetric flow rate compacts the air in the charge air pipe.

The compacting 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 distributor. Turbocharging is regulated by the boost pressure control. The boost pressure is regulated by the CDI control unit depending on the following values and associated assembly parts:

 Boost pressure sensor (B5/8)

 Coolant temperature sensor (B11/19)

 Charge air temperature sensor (B17/15)

 Temperature sensor upstream of ATL (B16/11)

 Intake manifold pressure sensor (B28/19)

 The injection quantity is defined by the injection duration of the fuel injectors (Y76) and the fuel pressure in the rails.

 Fuel pressure sensor (B4/17) for the fuel pressure in the rails

 Exhaust gas pressure sensor (B60/4), for the exhaust gas pressure in the exhaust system

 The crankshaft position sensor (B70/1) for the engine speed

 Atmospheric pressure sensor (integrated in CDI control unit), for recording the atmospheric pressure.

Function sequence for charging

After evaluating the input signals, the CDI control unit actuates the boost pressure regulator (Y77/8) by means of a pulse width modulated signal, dependent on the boost pressure characteristics map. The position of the guide vanes in the ATL 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 ATL rpm is used to determine the quantity of pre-compressed 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 exhaust gas turbocharger from thermal and mechanical overload, the CDI control unit monitors the exhaust gas temperature via the temperature sensor upstream of the exhaust gas turbocharger and the exhaust gas pressure via the exhaust gas pressure sensor. The boost pressure is reduced if there is any risk of thermal or mechanical overload.