1600 SRM 974
Description
General
This manual describes the disassembly and assem-
bly of the steering system for repairs. There is a de-
scription for each part of the steering system. The
steering system rotates the master drive unit (MDU)
to steer the lift truck. The steering pump for this sys-
tem also supplies oil to operate auxiliary hydraulic
functions when the lift truck has these functions.
The steering system for the narrow-aisle and gro-
cery-reach-series lift trucks features a hydrostatic
steering system.
This system utilizes a steering
control unit (SCU) and a hydraulic motor assembly.
The components are mounted inside the drive unit
compartment. The SCU is connected to the steering
disk. The steering disk is positioned for easy opera-
tion and requires only four and one-quarter turns to
obtain full steering of 180 degrees.
When the SCU is activated, hydraulic oil is directed
to the hydraulic motor assembly.
The hydraulic
motor assembly, mounted on the articulating axle
weldment, is connected to the MDU with a chain.
The hydraulic oil from the SCU drives the hydraulic
motor assembly to turn the MDU in the desired
direction.
WARNING
The narrow aisle and grocery reach series lift
trucks may be furnished with automotive or re-
verse steering. Before working on any of these
lift trucks, be sure of the type of steering that is
used on the lift truck being worked on. Reverse
steering may be obtained by reversing the two
hoses from the SCU to the steer motor assem-
bly.
The steering system draws hydraulic oil from the
same hydraulic tank used by the mast and reach as-
sembly. The hydraulic oil is directed to the SCU by
the power steering pump. This gear pump has a pri-
ority flow valve, which will provide hydraulic oil for
power steering first if both the power steering and
auxiliary functions are being used at the same time.
The gear pump is driven by a 24- or 36-volt perma-
nent magnet motor.
Description
The power steering system is a hydrostatic steering
system. See Figure 1. The control of the steering is
through a hydraulic circuit. An electric motor for the
steering pump is energized when the brake switch
and the operator sensing switch are closed and the
key switch is in the ON position. When the electric
pump motor operates the steering pump, hydraulic
oil flows through the power steering system. Moving
the steering disk rotates the shaft of the SCU. The
SCU meters the flow of oil to the hydraulic motor
on the axle weldment. The hydraulic motor moves
a chain to rotate the MDU and steer the lift truck.
When the steering disk is not being moved, the
hydraulic oil flows from the gear pump through the
excess flow port of the steering pump to the pro-
portional control valve for supplying the auxiliary
functions. If the auxiliary functions are not selected,
the oil is returned to the hydraulic tank.
When
the steering disk is being moved, the hydraulic oil
flows through the priority flow line from the gear
pump to the SCU, then to the hydraulic motor. This
hydraulic oil returns from the hydraulic motor to
the SCU, then to the hydraulic tank.
1.
STEERING DISK/ARM
2.
STEERING CONTROL UNIT (SCU)
3.
STEERING MOTOR
Figure 1. Typical Steering System
1