Boost pressure control, function

P09.40-2280-12

1 Turbocharger

2 Control rod

3 Vacuum cell

4 Air filter

B2/5 Hot film mass air flow sensor

G1 Battery

K40/1kF Gasoline/diesel engine relay

L8 Crankshaft rpm sensor

N3/10 Motor electronics control unit

Y77 Wastegate valve

Boost pressure control

Boost pressure control is performed electropneumatically via the wastegate valve and the boost pressure control valve integrated in the turbocharger.

The wastegate valve is actuated by the motor electronics control unit.

Function

The turbine wheel of the turbocharger is driven by the exhaust gas stream. As the exhaust gas quantity increases, the turbine wheel speed increases and thus the boost pressure. The boost pressure is matched to the actual load condition of the engine.

The vacuum cell actuates the boost pressure control valve (wastegate) via a control rod. If the boost pressure is too low, the vacuum cell closes the boost pressure control valve (wastegate) via spring force, the bypass is closed and the entire exhaust gas volume drives the turbine wheel.

The rising boost pressure affects the diaphragm of the vacuum cell via the wastegate valve.

The motor electronics control unit uses signals fro the hot film MAF sensor and signals from the crankshaft rpm sensor to calculate the corresponding boost pressure and actuates the wastegate valve. This opens the boost pressure control valve (wastegate) via the vacuum cell.

If the wastegate is open, part of the exhaust gas volume can bypass the turbine wheel and flow directly into the exhaust system. Thus the speed of the turbine wheel is reduced and therefore the boost pressure.