Charging, function

S09.00-4510-79

Function requirements for charging - general

 Circuit 87 (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 number of revolutions of the compressor wheel and the resulting high flow volume 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.

Charging 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 assembly parts:

 Boost pressure sensor (B5/1)

 Coolant temperature sensor (B11/4)

 Charge air temperature sensor (B17/8)

 Pressure sensor downstream of air filter (B28/5)

 The injection quantity, determined by the injection period of fuel injectors (Y76) and the fuel pressure in the rails. The fuel pressure in the rails is detected by the high pressure fuel pressure sensor (B4/6).

 Temperature sensor upstream of exhaust gas turbocharger(B19/11) for the exhaust gas temperature in the exhaust system

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

 Crankshaft Hall sensor (B70), for 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 control pressure transducer (Y77/1) by means of a pulse width modulated signal, dependent on the boost pressure characteristics map.

Over the control linkage over the boost pressure control pressure transducer the position of the guide vanes is adjusted in the ATL. The adjustable guide vanes modify the flow cross-section through which the exhaust gas flows to the turbine wheel. The turbine wheel thus matches the gas pressure present at the turbine to the required boost pressure.

The turbine speed of the turbine wheel is used to determine the amount 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 ATL from thermal and mechanical overload, the CDI control unit monitors the exhaust temperature via the temperature sensor upstream of the ATL and the exhaust pressure via the exhaust pressure sensor.

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