TM 5-6115-434-12
(e)
Engine electrical system (fig. 1-5). The engine electrical system is a 24v dc system which provides automatic
actuation in proper sequence of the various circuits which control engine starting, ignition, fuel flow, acceleration,
monitoring engine operation, and engine shutdown. The engine electrical system consists of the following components
together with interconnecting wiring and connectors: starter motor, centrifugal switch, oil pressure sequencing switch, low
oil pressure switch, ignition unit, igniter plug, fuel shutoff solenoid valve, load control valve solenoid, time totalizing
meter, circuit breaker, oil temperature bulb, exhaust gas temperature thermocouple, and tachometer-generator. When
energized, the starter motor rotates the engine gear train and compressor and turbine rotating parts Rising oil pressure
actuates the oil pressure sequencing switch to complete a circuit to open the fuel shutoff solenoid valve and energize the
ignition unit and igniter plug. At approximately 35-percent of engine governed speed, the starter cutout switch in the
centrifugal switch actuates to open the circuit to the starter motor. At approximately 95percent of engine governed
speed, 'the ready to load switch in the centrifugal switch is actuated and opens the circuit to the ignition unit and closes
the circuit of the time totalizing meter. If the engine should overspeed, the overspeed shutdown switch in the centrifugal
switch is actuated at 105 to 110-percent of engine governed speed and opens the circuit to the fuel shutoff solenoid valve
and stops the fuel flow to the combustion chamber to stop the engine. During engine starting, the low oil pressure switch
is actuated by increasing oil pressure and completes a holding circuit which is opened to shutoff fuel flow if oil pressure
drops below minimum pressure during engine operation.
(f)
Lubrication system (fig. 1-6). The engine lubrication system provides pressurized spray and splash
lubrication for the gears, shafts, and bearings in the engine. The lubrication system consists of the following components
together with interconnecting lines and fittings; an oil pump assembly with integral pressure and scavenge pumps and a
filter element, oil temperature bulb, oil jet and scavenge fittings, cooling air fan, oil temperature regulator (oil cooler) oil
tank, dual pad drive assembly scavenge pump, and low oil pressure switch. The oil pump assembly pumps oil from the
oil tank through a filter to the oil jets on the engine. Scavenge oil is pumped from the engine scavenge areas to the oil
temperature regulator (oil cooler), where a thermostatic valve bypasses the oil through the oil cooler tubes, if required,
then returns the cooled oil ,to the oil tank. The scavenge oil pump on the dual pad drive assembly returns scavenge oil
from the drive assembly sump to the oil tank. The cooling air fan directs a portion of the cooling air flow through a duct
to the tubes in the oil temperature regulator (oil cooler). The remaining cooling air developed by the cooling fan is ducted
to the 400 Hz generator. The low oil pressure switch provides for shutdown of the. engine in the event oil pressure
should drop below minimum pressure during engine operation.
c.
Power Unit Electrical System (fig. 1-7 and 1-8). The power unit electrical system consists of a 24v dc system
powered by batteries, a 120/240v ac single phase, 60 Hz system powered by the engine driven 60 Hz generator, and a
120/208v ac three phase, 400 Hz system powered by the engine driven 400 Hz generator. The 24v dc system provides
power for engine starting and control, control power for the other power unit systems (electrical, conditioned air and
water) control components, and emergency lighting power for other elements of the MUST hospital. The 24v dc
emergency light power is distributed through the 60 Hz system convenience receptacles and cable assemblies. The 60
Hz system provides 60 Hz power to elements of the MUST hospital as required. The 400 Hz system provides 400 Hz
power for operation of the conditioned air system, water pumps, water hose heating, battery charging, and for 400 Hz
power requirements for other elements of the MUST hospital. All of the electrical systems incorporate safety devices to
disconnect the electrical output and prevent damage to components in the event of an overload, undervoltage,
overvoltage, or
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