February_2022 - 27

3 and 4). Medium allows for four of the cylinders to provide
engine-braking capability (cylinders 1, 2, 5, and 6). High allows
for all six cylinders to provide engine braking.
HOW IS THE GOAL ACCOMPLISHED?
Now that I have an understanding of the system's goal, I can begin
to understand how that goal is carried out. The first thing we have
to understand is that this Caterpillar uses mechanical electronic
unit injectors (MEUI). The engine's camshaft has an additional
lobe (for each cylinder) to operate an intensifier piston on top of
the injector itself (Figure 1). The ECM will command the injector
solenoid on/closed to trap the fuel in the injector. The cam
lobe will operate the rocker/piston and with the injector solenoid
energized the trapped fuel will be pressurized and delivered to
the combustion chamber. When the solenoid is off, fuel is not
trapped but vented from the injector to a return fuel circuit.
It's this same rocker that is used to operate the injector piston
that is also used to operate the engine brake system. As the
rocker is driven by the camshaft, it pivots on a fulcrum, like any
other rocker. The camshaft-side lifts and the injector-side travels
down (like a seesaw). It's the upward motion of the rocker that
drives a pushrod connected to a master hydraulic cylinder. This
system diagram is drawn in a state of " engine-brake operation "
and demonstrates only one cylinder's circuit but functionality
is the same for all six cylinders.
SYSTEM OPERATION
Pressurized oil is supplied from the engine. During normal operation
of the engine, the oil is vented back through the oil drain
circuit via the de-energized solenoid control valve. However,
when engine-braking is called upon, the solenoid control valve
is energized by an ECM and allows supplied oil to reach the
hydraulic control valve which is being held closed by a spring.
As the pressure of the supply oil overcomes the spring tension
of the hydraulic control valve, the valve begins to shuttle and
unseats the check-ball as well. Supply oil is then allowed to fill/
feed the hydraulic circuits of the master and slave cylinders. This
will cause the master cylinder pushrod to extend and come into
contact with the injector rocker at the camshaft (as indicated by
the yellow arrow in Figure 1).
The motion of the cam lobe operates the injector rocker and
drives the pushrod of the master cylinder up. As a result, the oil in
the feed circuits is displaced, and the check-ball in the hydraulic
control valve seats. Pressure begins to increase in the hydraulic
circuits as the oil is now trapped and the master cylinder pushrod
is displaced by the rocker.
The movement of the master cylinder pushrod is transferred
in the hydraulic circuit to the slave cylinder and it extends to
operate the exhaust valve rocker (as indicated by the pink-colored
star in Figure 1). Compression is vented to the exhaust stream
and the valve will close as the lobe of the injector rocker rotates
past its apex.
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www.VehicleServicePros.com FEBRUARY 2022 PROFESSIONAL TOOL & EQUIPMENT NEWS
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February_2022

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