22 1 ENGINE SYSTEMS
VGT Closed Loop System
Figure 13 VGT closed loop system
The Variable Geom e try Turbocharger (VGT) is a
closed loop system that uses the Exhaust Back
Pressure (EBP) sensor to provide f eedback to the
ECM. The ECM uses the EBP sensor to continuously
monitor EBP and adjust the duty cycle to the VGT to
match engine requirements.
VGT Control
Figure 14 VGT control
The VGT actuator is a control module that contains
a microchip and a DC motor. The VGT actuator
is located below the turbocharger. The microchip
operates a D C motor which rotates a crank lever
controlling the va ne position in th e t urbine housing .
The position of the vanes is based off the pulse-width
modulated signal sent from the ECM.
Actuated vanes are m ounted around the inside
circumference of the turbine housing. A unison ring
links all the vanes. When the unison ring moves,
all vanes move to the same position. Unison ring
movement occurs when the c rank lever in the control
module moves.
Exhaust gas flow can be regulated depending on
required exhaust back pressure for engine speed
and load. As demand for EBP increases, the ECM
increases the pulse-width modulation to the VGT
control module. W hen EBP demand decreases, the
ECM decreases the duty cycle to the control module.
EGES-270-1
Read all safety instructions in the "Safety Information" section of this manual before doing any procedures.
Follow all warnings, cautions, and notes.
© August 2008 Navistar, Inc.
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