Charging, function

Function requirements for charging - general

 Circuit 87 ON (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 rotational speed 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 (N39) depending on signals from the following components:

 Boost pressure sensor (B5/1)

 Coolant temperature sensor (B11/4)

 Charge air temperature sensor (B17/8)

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

 CAT temperature sensor (B19)

 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 rail pressure sensor (B4/6).

 Exhaust back pressure sensor (B60) (model 164) or exhaust pressure sensor (B60) (model 251)

 Crankshaft Hall sensor (B70), for the engine speed

 atmospheric pressure sensor, for acquisition of the atmospheric pressure

Function sequence for charging

After evaluating the input signals, the CDI control unit actuates the boost pressure regulator (Y77/1) 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 monitored by the boost pressure sensor and passed on to the CDI control unit. The exhaust back pressure is monitored by the exhaust back pressure sensor (model 164) or exhaust pressure sensor (model 251) by the CDI control unit as protection against thermal and mechanical overload of the ATL. The boost pressure is reduced if there is any risk of thermal or mechanical overload.