Paccar PX-9, Operator'S Manual

Page: 22 / 97

This feature, if the vehicle is equipped,
allows the VGT to act as an exhaust brake.
An engine exhaust brake retards the speed
of the engine during motoring conditions to
provide additional vehicle braking power
and extend the life of the vehicle service
brakes.
An engine exhaust brake functions by
retarding engine speed by creating high
exhaust back pressure. This back pressure
is obtained by restricting air flow through
the turbine housing of the turbocharger.
This restriction through the turbine housing
of the turbocharger is created through
positioning of the sliding nozzle located
internally to the VGT. The position of the
sliding nozzle is controlled by the engine
control module (ECM).
When the engine exhaust brake switch is
in the ON position, the ECM monitors
inputs (such as accelerator pedal position
and engine speed). From these inputs, the
ECM determines when to enable the
engine exhaust brake feature when the
proper braking conditions are present.
Other features/switches like cruise control,
can also affect when the engine exhaust
brake activates. For more information on
how the engine exhaust brake functions,
refer to the equipment manufacturer
service information or contact a Cummins®
Authorized Repair Location.
NOTE
The exhaust brake can only be activat-
ed when the accelerator pedal is at its
low idle position. With the throttle at
low idle position, fueling commands to
the cylinders will
not
detract from the
braking power of the brake system.
NOTE
The engine exhaust brake is designed
to assist the vehicle service brakes
when slowing the vehicle to a stop.
Service brakes will be required to bring the
vehicle to a stop.
Vehicle service brakes must be used when
additional braking power is required.
CAUTION
Never exceed governed engine speed
because engine damage can occur.
Operating the engine beyond the gov-
erned speed causes additional strain
on valve train and internal engine com-
ponents. Operate the engine within
governed engine speed.
The optimum braking power of the engine
exhaust brake is reached at rated engine
speed. Correct gear selection, therefore, is
critical.
CAUTION
Exceeding governed engine speed
can cause engine damage. Operating
the engine beyond the maximum en-
gine speed may cause serious engine
damage and is considered engine
abuse. Use the engine and vehicle
braking systems to control engine
speed.
ENGINE OPERATION - Operating Instructions
Y53-1185-1J1 (10/21) 19
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