Subaru 2002 Impreza Service Manual page 140

TURBOCHARGER SYSTEM
Intake (Induction)
When the supercharging pressure reaches the predetermined level, the wastegate controller lets
the supercharging pressure press the diaphragm. This causes the wastegate valve to open
through a linkage. With the wastegate valve open, part of the exhaust gas is allowed to flow into
the exhaust gas pipe that bypasses the passage to the turbine.
This decreases the exhaust gas pressure that rotates the turbine and keeps the supercharging
pressure constant.
0
It means
P2
-
P1 =
constant.
PI:
Atmospheric pressure
P2:
Supercharging pressure
NF0349
2. CONCEPT OF THE WASTEGATE VALVE CONTROL
At high altitudes, the atmospheric pressure
(PI)
is low, so that the supercharging pressure
(P2)
is also low in a conventional system. The wastegate solenoid valve operates in such a way that
a constant supercharging pressure
(P2)
is maintained by acting in response to change in the atmo-
spheric pressure.
NF0350
IN-8