Charging, function

Function requirements for charging - general

 "Circuit 87M ON" (engine timing "ON")

 "Circuit 61 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 turbocharger. The turbocharger 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 volume flow compacts the air in the charge air pipe. The compaction 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 manifold.

Turbocharging is regulated by the boost pressure control.

The boost pressure is regulated by the CDI control unit (N3/30) (engine 642.8) or CDI control unit (N3/20) (engine 642.9) dependent on the following values and the associated components:

– boost pressure sensor (B5/8) (engine 642.8) or boost pressure sensor (B5/1) (engine 642.9)

– coolant temperature sensor (B11/19) (engine 642.8) or coolant temperature sensor (B11) (engine 642.9)

– charge air temperature sensor (B17/15) (engine 642.8) or charge air temperature sensor (B17/9) (engine 642.9)

– intake manifold pressure sensor (B28/19) (engine 642.8) or intake manifold pressure sensor (B28) (engine 642.9)

– temperature sensor upstream of turbocharger (B16/11)

– injection quantity, determined over the injection time of cylinder 1 injector (Y76/18) (engine 642.8) or cylinder 1 injector (Y76/1) (engine 642.9), cylinder 2 injector (Y76/19) (engine 642.8) or cylinder 2 injector (Y76/2) (engine 642.9), cylinder 3 injector (Y76/20) (engine 642.8) or cylinder 3 injector (Y76/3) (engine 642.9), cylinder 4 injector (Y76/21) (engine 642.8) or cylinder 4 injector (Y76/4) (engine 642.9), cylinder 5 injector (Y76/22) (engine 642.8) or cylinder 5 injector (Y76/5) (engine 642.9), cylinder 6 injector (Y76/23) (engine 642.8) or cylinder 6 injector (Y76/6) (engine 642.9) and from the fuel pressure in the rails. The fuel pressure in the rails is recorded over the fuel pressure sensor (B4/17) (engine 642.8) or rail pressure sensor (B4/6) (engine 642.9).

– exhaust back pressure sensor (B60/4) (engine 642.8) or exhaust back pressure sensor (B60) (engine 642.9), for the exhaust pressure in the exhaust system

– crankshaft position sensor (B70/1) (engine 642.8) or crankshaft sensor (L5) (engine 642.9), for the engine speed

- atmospheric pressure sensor, for acquisition of the atmospheric pressure

Function sequence for charging

After evaluation of the input signal the CDI control unit actuates the boost pressure regulator (Y77/8) (engine 642.8) or the boost pressure regulator (Y77/1) (engine 642.9) by means of a pulse width modulated signal (PWM signal), based on the boost pressure characteristics map. 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 rotational speed 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 turbocharger from thermal and mechanical overload, the CDI control unit monitors the exhaust temperature via the temperature sensor upstream of the turbocharger and the exhaust back pressure through the exhaust back pressure sensor (engine 642.8) or the exhaust back pressure sensor (engine 642.9).

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