Figure 1-3. Charging System Basic Schematic

TM 10-3930-623-12

1-6. The forklift trucks are powered by Continental FS-

244 Military Standard engines rated at 82.3 horsepower

when operating at 2800 revolutions per minute.

1-7. DETAILED DESCRIPTION.

1-8. ENGINES (See figure 1-2). Differences between

the engines used in the trucks are mainly in parts

dimensions.

The details given in subsequent

paragraphs apply to all trucks unless otherwise stated.

1-9. The full pressure lubrication system includes a

gear-type oil pump with adjustable bypass valve to

maintain suitable pressure through all speeds, and a

replaceable element oil filter.

1-10. The fuel system includes a mechanical diaphragm

fuel pump, driven by the engine camshaft, a single

venturi updraft carburetor, and a mechanical governor

which limits the maximum speed of the engine by closing

the carburetor throttle valve when the engine reaches

the governed speed. The carburetor air cleaner uses a

disposable paper filter element.

1-11. ALTERNATOR. The alternator is an ac generator

designed and constructed to give long service with a

minimum of maintenance. The rotor is mounted on a

ball bearing at the drive end, and a roller bearing at the

Figure 1-3. Charging System Basic Schematic

slip ring end, and each bearing has a grease supply

which eliminates the need for periodic lubrication. Two

of the alternator provides the magnetic field for the

brushes are used to carry current through the two slip

alternator. When the engine is started, the alternator

rings to the field coil which is mounted on the rotor. The

builds up voltage. This causes current to flow to charge

brushes are extra long and under normal operating

the battery and/or power accessories.

conditions will provide long periods of service. The

stator windings are assembled on the inside of a

2. As alternator speed increases or the accessory

laminated core that forms part of the frame. Six rectifies

load decreases, alternator voltage builds up to a

diodes, mounted in the slip ring end frame, are

predetermined value at which the regulator is set or

connected to the stator windings. The six diodes change

adjusted. The electrical control portion of the regulator

the ac voltage to de voltage which appears at the BAT

then places a higher voltage on the base of the transistor

terminal on the alternator. A capacitor, or condenser,

than is impressed upon the emitter, and the transistor is

mounted in the end frame protects the diodes from high

voltages. Current output of the alternator is self-limiting

turned "off". With no current flow in the emitter-collector

by design to its rated maximum, regardless of speed or

circuit, there is no current flow in the field coil of the

external circuit conditions.

An externally mounted

alternator. As a result, alternator voltage drops below

voltage regulator limits the operating voltage to a

the setting or adjustment of the regulator.

specified value through the full speed range of the

alternator. Figure 1-3 shows a schematic view of the

3. Then the electrical control portion of the

alternator and regulator.

regulator places a lower voltage on the base of the

1-12. VOLTAGE REGULATOR. The transistor is an

transistor than that on the emitter, and the transistor is

electrical device made of semiconductor materials which

again turned "on". With current flow again in the

is used as a switch to control the alternator field current

emitter-collector and field coil circuit, the magnetic field

in order that alternator voltage can be limited to a proper

is reestablished in the alternator, and alternator voltage

value. Figure 1-3 is a greatly simplified diagram of the

can again build up to the setting of the regulator.

alternator and regulator circuit. A brief description of the

operation follows:

4. Thus, the switching "on" and "off' of the

1. When the ignition switch is closed, battery

transistor regulates the amount of field current supplied

voltage supplies current through the emitter (E) and

to the alternator. The frequency of this switching is

collector (C) of the transistor to the field coil of the

dependent primarily upon the accessory load and

alternator. This emitter-collector circuit is complete since

alternator speed. Under certain conditions the "on" and

the transistor is turned "on" by a higher voltage on the

"off" cycle is repeated as much as 7,000 times per

emitter than on the base (B), which permits emitter-base

second.

current to flow. The flow of current to the field circuit

1-3