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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 small turbocharger,
increasing the wheel speed quickly at low speed.
• 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.
• The closed vane position is also used
for cold ambient warm up.
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 position 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: There is actually an infinite number of vane
positions between open and closed. The partially
closed picture is for illustration purposes only.
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 with minimal restriction.
AIR MAnAgeMent SySteM
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