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).

 The engine speed via the crankshaft position sensor (L5).

 The injection quantity, which is determined by the injection timing of the 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).

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Following evaluation of the input signals, the CDI control unit actuates the right boost pressure positioner (Y100/1) according to the boost pressure performance map with a PWM signal. The position of the guide vanes in the turbocharger is determined by the control rods of the right boost pressure positioner. 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.

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Engine and turbocharger protection

To prevent damage to the engine and turbocharger caused by overheating, the exhaust back pressure is monitored by the exhaust back pressure sensor (B60).

At a high exhaust back pressure the CDI control unit reduces the boost pressure and the injection quantity to protect the turbocharger and engine.