Audi A3 Sportback, Сервисная инструкция, Страница: 32 / 60

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Engine
332_012
Air divert control in overrun
If the throttle valve is closed when the engine is in overrun, a back pressure will develop in the compressor
housing due to the continuing presence of boost pressure. This back pressure noticeably reduces the speed
of the compressor wheel, the net result of which is in a reduction in boost pressure and increased turbo lag.
To avoid this, the turbocharger divert air valve N249 is opened by an electrical actuator. The valve opens a
bypass which allows the compressed air to flow back to the intake side of the compressor circuit via the
compressor wheel. In this way, the required turbine speed is maintained. The turbocharger divert air valve
N249 closes when the throttle valve opens and the boost pressure is immediately available again.
Overrun mode
Air intake
from air filter
Engine running under load
Divert air valve open
Divert air valve
closed