forklift trucks (fig. 5-37, view A). Figure 5-37, view B,
power to the drive motor over a given period of time.
shows a smaller electric forklift that has both steering
Most forklifts have speed controls that are incremental
and drive provided by the rear wheels. A 36- or 24-volt
type of controllers. In incremental controllers, a bank
storage battery is required to furnish power for the
of resistors is inserted into or shorted out of the circuit
traveling, the lifting, and the steering mechanism.
to obtain speed control. The stepless type in the newest
forklift trucks uses SCR control circuitry. The
The drive mechanism includes an electric drive
incremental type of truck control is similar to a car with
(traaction) motor, coupling, power axle assembly, and
a standard shift, and the stepless type of control is similar
control. Control of the travel circuit provides one
to a car with an automatic transmission that provides for
automatic accelerating speed plus four forward and four
smooth control of the speed.
reverse controlled speeds.
Many of today's shipboard requirements for
The lifting mechanism includes an electric motor,
material-handling operations necessitate very smooth
hydraulic pump, hydraulic fluid reservoir, hoist, tilt, side
acceleration of the electric truck. Smooth acceleration
shift cylinders, directional control valve, forks, and
for a major portion of the speed range is highly desirable
controls.
and permits accurate maneuvering of the truck for
The vehicle steering system consists of a steering
spotting loads in congested areas.
motor, pump, steering gear assembly, power steering
The electrical system of an electric forklift maybe
unit, trailing axle, and controls.
logically divided into a power circuit and a control
The brake system consists of a master cylinder,
circuit. These two circuits comprise the circuitry for the
mechanical parking brake, and hydraulic service brakes.
hydraulic pump motor, the steer motor, and the drive
The operator controls the truck speed by depressing
motor. Figure 5-38 shows the wiring diagram of an
the accelerator pedal, which determines the amount of
electric forklift. Please refer to this figure as you read
Figure 5-38.--Wiring diagram of an electric forklift.
5-56
