THEORY OF OPERATION INTRODUCTION
This work package provides a functional description of the major systems found on the D6K Dozer. It also
describes how these systems interact.
The D6K Dozer is an earth-moving machine with a bulldozing attachment that cuts, moves, and grades material
through forward motion of the machine. A 6.6 L diesel engine powers the D6K Dozer. Additional attachments for
the machine include a hydraulically operated ripper and a towing winch.
Refer to the Theory of Operation work packages for information about the following systems:
This includes the engine, engine Electronic Control Module (ECM), engine ECM inputs and outputs, air
cleaner, turbocharger, engine aftercooler, fuel system, ether injection, cooling system, and engine lubrication
2. MACHINE ELECTRICAL
This includes the machine Electronic Control Module (ECM), machine ECM inputs and outputs, equipment
ECM, Machine Security System (MSS), batteries, alternator, and starting motor.
The monitoring system includes an indicator and gauge display and a messenger display. The indicator and
gauge display is located in the instrument cluster. The messenger display is located to the right of the operator.
The Messenger monitoring system provides supplemental information, warnings, and instructions to the oper-
ator. It also provides an interface with some electronic machine functions. The monitoring system consists of
software and hardware components.
Hydraulic Fan System The hydraulic fan system uses a fixed-displacement hydraulic pump to drive a fixed-
displacement fan drive gear motor. The fan system has variable speeds, even though the pump and motor
have fixed displacements. The demand fan solenoid in the fan control manifold controls the flow of hydraulic oil
to the fan motor, which controls fan speed. The machine ECM determines the proper fan operation based on
hydraulic oil temperature, engine coolant temperature, and inlet manifold temperature.
Powertrain The hydrostatic powertrain is a dual path hydrostatic transmission with high-pressure closed
drive loops. Each drive loop contains a piston pump and piston motor for each track. The dual path system
allows the machine to perform pivot turns and to counterrotate. The piston pumps are overcenter pumps that
provide oil flow for forward and reverse travel. The direction of oil flow from the piston pump determines travel
direction. The piston pumps also affect the machine's ground speed. First, the pumps upstroke to provide the
desired speed; then, the piston motors will destroke if the operator commands more speed. The piston motors
are infinitely variable and provide a range of ground speeds.
Electronic Hystat Control System In response to operator and sensor input, the electronic hystat control
system controls the following: displacements of the hydrostatic drive pumps and motors; the backup alarm out-
put; the hydrostatic transmission override valve state; the parking brake valve state; the engine start and neu-
tral interlock; the electronic fuel pump; the maximum speed indicator; the ether starting aid; and the engine
inlet air heater. The system also provides engine overspeed and underspeed protection. In an overspeed con-
dition, the system automatically adjusts the current supplied to the hydrostatic transmission pumps and motors
to slow the machine. In an underspeed condition, the system decreases control currents to the hydrostatic
transmission pumps and motors in response to the low engine speeds and engine lug.