TM 9-2350-277-34
THEORY OF OPERATION — Continued
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The variable speed fan drive system is designed to modulate the cooling fan speed to maintain relatively constant coolant
temperatures despite vehicle load or ambient temperature. The cooling fan speed is controlled by the fan drive assembly. The
fan drive assembly is driven by the engine crankshaft through a splined coupling. The fan drive assembly contains a
multi-plate clutch pack which regulates the fan drive output speed. The thermostatic control valve senses engine coolant
temperature and regulates the hydraulic pressure to the fan drive assembly clutch pack. The higher the coolant temperature,
the higher the hydraulic pressure which will result in less clutch slip and higher fan speed.
The surge tank acts as an overflow tank to keep the cooling system from overpressurizing. It also removes air from the engine
coolant. There is a low coolant level transmitter to signal the operator if more coolant is needed.
ENGINE AIR SYSTEM
The engine air system allows air to enter the engine. The air cleaner cleans air that enters the engine. Dust is drawn out
through a scavenge outlet. Air is filtered through a reusable filter element before delivery to the engine. An air filter indicator
shows when the element is clogged and needs cleaning or replacing. After being filtered, the air moves through the
turbocharger and into the engine cylinders.
AUXILIARY AUTOMOTIVE SYSTEMS
The auxiliary automotive systems include driver controls, fuel cells, personnel heater, and bilge pumps. Also there is a crew
ventilation system, and fire suppression system.
DRIVER CONTROLS
The driver controls regulate the engine, transmission, and steering braking systems of the carrier.
The fuel shutoff control is used to stop the supply of fuel to the fuel pump. To start the engine, the driver must open the valve.
The throttle linkages are used to control the engine speed. The gear selector allows the driver to choose the proper gear for the
carrier. The steering system controls the carrier direction. The steering control consists of a steering yoke and linkage
connected to the transmission.
The brake system allows the driver to stop a moving carrier and hold the carrier in position. The braking system consists of
the service brake and the parking brake. The service brakes are hydraulic and applied by pedal. The parking brake
mechanically locks the transmission to prevent carrier movement. Also, the system has levers, rods, shafts, and linkages
connecting to the transmission brake shaft.
FUEL TANKS
Diesel fuel is stored in two separate fuel tanks. They are located on the back of the carrier hull. The fuel is drawn from the
fuel tanks through the primary fuel filter by the fuel pump. The fuel then flows through the secondary fuel filter to the
injectors. The injectors regulate the amount of fuel that enters the engine.
PERSONNEL HEATER
The personnel heater system provides heat inside the carrier. Major parts are the combination combustion chamber/heat
exchanger, blowers, a fuel pump, and an electrical control and safety system. The heater operates using diesel fuel drawn
from the fuel tanks. Fuel is delivered to the combustion chamber from the fuel pump. Outside air is drawn into the
combustion chamber by one of the blowers. A blower draws air from the crew compartment into the combustion chamber.
The air is warmed by heat from the combustion process and then returned to the crew compartment.
BILGE PUMPS
Two electrically driven bilge pumps remove water and other liquids from the hull. Water enters the pumps through a screened
inlet. The pumps force water out of the carrier through outlet tubes. The bilge pumps are controlled by a switch on the
driver’s instrument panel.
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