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 the air filter (B28/5).

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

 The injection quantity 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 is adjusted by the control linkage of the boost pressure positioner. Adjustable guide vanes modify the flow cross-section through which the exhaust gas flows to the turbine. In this way the gas pressure in the turbine is adjusted to the requested boost pressure. The turbocharger speed is used to determine the quantity of compress air and thus the boost pressure. The boost pressure is constantly being monitored by the boost pressure sensor (B5/1) and passed on to the CDI control unit.