Boost pressure control, function

The boost pressure control controls turbocharger charging and is regulated by the CDI control unit (N3/9) depending on the following associated components:

 Coolant temperature via the coolant temperature sensor (B11/4).

 Charge air temperature via the charge air temperature sensor (B17/8).

 Atmospheric pressure, via the pressure sensor downstream of air filter (B28/5) (except model 463) or pressure sensor downstream of air filter, right cylinder bank (B28/5) (model 463).

 Engine speed via the crankshaft Hall sensor (B70).

 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).

After evaluating the input signals, the CDI control unit actuates depending on the charge pressure performance map of the boost pressure positioner (Y77/1) by means of a pulse width modulation (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 boost pressure sensor (B5/1) and transmitted to the CDI control unit.