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A I R M A N A G E M E N T S Y S T E M
VGT Turbine Vanes Closed
• During engine operation at low engine
speeds and load, little energy is available
from the exhaust to generate boost. In order
to maximize the use of the energy that is
available, the vanes are closed. In doing so,
the exhaust gas is accelerated between the
vanes and across the turbine wheel. In
general, this allows the turbocharger to
behave as a smaller turbocharger than it
actually is.
• Closing the vanes also increases the back
pressure in the exhaust manifold which is
used to drive the exhaust gas through the
EGR cooler and valve into the intake
manifold. This is also the position for cold
ambient warm up.
VGT Turbine Vanes Partially Closed
• During Engine operation at moderate engine
speeds and load, the vanes are commanded
partially open.
• The vanes are set to this intermediate posi-
tion to supply the correct amount of boost to
the engine for optimal combustion as well as
providing the necessary back pressure to
drive EGR.
• Note: The VGT control valve piston is
coupled to the vanes through a shaft and
the unison ring.
VGT Turbine Vanes Open
• During engine operation at high engine
speeds and load, there is a great deal of
energy available in the exhaust.
• Excessive boost under high speed, high load
conditions can negatively affect component
durability, therefore the vanes are
commanded open preventing turbocharger
overspeed.
• Essentially, this allows the turbocharger to
act as a large turbocharger.
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ACTUATOR PISTON
UNISON RING
ACTUATOR PISTON
UNISON RING
VANES
ACTUATOR PISTON
UNISON RING
VANES
73
74
VANES
75
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