STEERING SYSTEM 5540F/YB5515 SERVICE MANUAL
10-6 Published 10-21-2010, Control# 198-04
UNITS WITH RETURN-TO-CENTER STEERING
TECHNICAL DATA
Rated pump output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9.8 gpm at 2500 rpm (37,1 L/min at 2500 rpm)
Relief valve setting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2500 ± 50 psi at 2500 rpm (17 225 ± 345 kPa at 2500 rpm)
Steering Proximity Switch Setting . . . . . . . . . . . . . . . . . . . . .1/8 - 7/32 inch (3,2 - 5,6 mm)
DESCRIPTION
General
The main components of the steering system are the second
section of the secondary hydraulic pump Figure 10-6, the
priority flow control valve, the load sensing steering orbitrol,
hydraulic tank, one front steering cylinder, two rear steering
cylinders and the steering select valve.
When the steering wheel is turned, a pressure demand is
sensed by the priority flow control valve through load sensing
line between the priority flow control valve and the flow
sensing steering orbitrol.
Oil from the second section of the secondary hydraulic pump
is then distributed through the priority flow control valve and
a check valve to the steering orbitrol.
When a turn is made, oil is distributed from the steering
orbitrol directly through the steering select valve and/or to
the steering cylinders.
When the steering orbitrol is neutral, the load sense signal is
ceased, full pump flow is then distributed to the outrigger and
brake circuits through the priority flow control valve.
Maximum steering system pressure is controlled by a relief
valve in the priority flow control valve.
Steering Modes
The crane can be operated in three steering modes. These
modes are selected using the steering selector switch
located to the right of the operator on the side instrument
panel. The three modes are:
• Two-wheel steering
• Four-wheel steering
• Crab steering
Two-Wheel Steering
During two-wheel steering, the front wheels steer in the
same direction that the steering wheel turns. The rear
wheels remain in a fixed forward position.
When turning to the right Figure 10-7, hydraulic oil under
pressure from the steering pump flows through the priority
flow control valve to the P port of the steering orbitrol in the
operator’s compartment. When the steering wheel is turned
to the right, hydraulic fluid is directed through port R of the
steering orbitrol to port P of the steering select valve. The
steering select valve has four solenoid valves. These valves
are activated by the steering select switch in the operators
compartment. When the steering select switch is placed in
the two-wheel steering mode solenoid A is actuated. Oil
passes through the porting of the valve block to the base end
of the front axle steering cylinder. The piston moves to the
left, extending the left cylinder rod and retracting the right
cylinder rod, creating a right turn. Return oil from the steering
cylinder flows into port L, out of port T of the steering orbitrol
and back to tank.
Reference Only
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