THEORY OF OPERATION
The scraper consists of the following functional systems: engine; powertrain; air and brake systems; electrical system;
and steering and scraper hydraulic systems.
This work package explains how the systems and components of the machine work together. A functional description is
provided for each major component and system.
General. The tractor is equipped with a CaterpillarŪ 3406 turbocharged diesel engine with six in-line cylinders, gener-
Fuel System. The engine is powered with a direct fuel injection system. Fuel from the fuel tank is pulled through two
secondary fuel filters by the fuel transfer pump that is an integral part of the engine governor. Drilled passages in the
cylinder head provide continuous flow of fuel to the injectors. Unused fuel is returned to the fuel tank.
Cooling System. The cooling system consists of a belt-driven circulating water pump, 197°F (92°C) thermostat for con-
trolling coolant flow, engine-driven fan, oil cooler and radiator. The cooling system cools the engine by circulating pres-
surized ethylene glycol based coolant through the engine and radiator.
Lubrication System. The engine lubrication system consists of a gear-driven oil pump, oil filter, oil cooler and oil pan.
The engine is lubricated by cooled and pressurized oil which is circulated through the engine block and head.
Exhaust System. The exhaust system removes exhaust gases from the engine through the exhaust manifold and turbo-
charger. The gases flow into exhaust pipes and a muffler to the atmosphere above the cab.
General. Power from the engine is sent to the torque converter. The converter output is connected to the upper drive
shaft that moves the power to the eight-speed powershift transmission. The transmission is connected to transfer gears
that direct the power via the lower drive shaft to the differential in the drive axle. The differential and drive axles pro-
vide the power to the planetary carriers in the left and right final drives.
Transmission. The transmission has eight hydraulically activated clutches that provide eight speeds forward and one
Transfer Gears. The transfer drive gear receives power from the transmission output and transfers the power via a
transfer gear and shaft to the drive shaft yoke that is connected to the lower drive shaft.
Differential. The differential divides the balance of power that is sent to the final drives and wheels. When the machine
is turning, the differential allows the inside wheel to turn at a slower rate than the outside wheel. However, the differen-
tial still sends the same torque to each wheel.
Differential Lock. The differential lock is utilized when maximum traction is needed. The operator engages the differ-
ential lock by pressing down and holding the differential lock pedal. This in turn allows air pressure to engage the lock;
when the pedal is released, internal springs will disengage the lock. The differential lock should never be engaged when
one tractor wheel is spinning or when operator is turning (steering) machine; this action would result in damage to the