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is connected to the low-pressure compressor outlet
and uses engine coolant to regulate the charge air
temperature. The ISC air outlet is connected to the
compressor inlet on the high-pressure turbocharger.
High-Pressure Charge Air Cooler (HPCAC)
The HPCAC is installed between the high-pressure
turbocharger compressor outlet and the Engine
Throttle Valve (ETV). The HPCAC uses ambient air
flow to regulate the charge air temperature.
HPCAC air outlet is connected to the ETV body.
Air Control Valve
Figure 10 Air control valve
1.
To high-pressure turbocharger wastegate actuator
2.
Turbocharger 1 Turbine Output Pressure (TC1TOP)
input to sensor
3.
Compressed regulated air supply from chassis air
tank
ENGINE SYSTEMS
The air control valve controls air pressure to the
high-pressure wastegate actuator based on turbine
output pressure from a port on the output of the
low-pressure turbocharger.
pressure sensor is integral to the air control valve. Air
pressure to the air control valve is supplied from an
air tank mounted on the chassis. The air control valve
is controlled by the Engine Control Module (ECM).
The air control valve is normally closed. Thus, with no
Pulse Width Modulated (PWM) signal, the air control
The
valve remains closed and no air pressure is supplied
to the wastegate actuator on the high-pressure
turbocharger. When a decrease in charge air pressure
is required, the ECM supplies a PWM ground voltage
to the negative side of the wastegate control solenoid.
The other side of the wastegate control solenoid is
connected to 12V supply voltage. This causes the air
control valve to open which supplies air pressure to
the wastegate actuator.
The limit values of the PWM signal are between
approximately 95%, corresponding to an open air
control valve, and 5%, corresponding to a closed air
control valve. When the air control valve closes, it
interrupts the air supply to the wastegate actuator
and at the same time relieves air pressure from the
wastegate by allowing it to vent to atmosphere. The
wastegate actuator then closes, resulting in increased
charge air pressure.
19
The turbine output
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