Reference
Only
INTRODUCTION
999 SERVICE/MAINTENANCE MANUAL
1-18
Published 05-16-17, Control # 233-03
TRAVEL SYSTEM OPERATION
See Figures
Travel
handles (1) or foot pedals (2) are inoperable when
travel brakes (3) are spring-applied, and there is no PC
output signal to right travel pump EDC (4) or left travel pump
(5) EDC. When travel brakes are released, travel handles or
foot pedals are operable.
For travel operation, charge pressure from rear drum pump
must be above 200 psi (14 bar) for travel spring brakes to
fully release. If travel charge pressure is below above
pressure, travel brake could be partially spring-applied and
damage the brake. The left travel charge pump (14) supplies
pilot charge pressure for enabling boom hoist, front drum,
and rear drum motor servo operation.
To ensure crane travels in a straight forward or reverse
direction, both travel hydraulic drive systems have shuttle
valves (6) and pressure senders (7) that monitor the
pressure to both closed-loop systems. When traveling, the
PC monitors signals from pressure senders and adjusts
displacement of the travel pumps (8) to maintain equal
pressure in each travel drive system. This allows crane to
track in a controlled straight direction.
Continuous changing of closed-loop fluid occurs through
leakage in motors (9) and loop flushing valves (10) that allow
6 GPM (23 L/min) of fluid to return to tank when system
pressure is above 350 psi (24 bar).
Travel Brakes
When travel brake switch (11) is in on - park
position, both
right and left travel brakes are spring-applied to hold crane in
position. Travel brake release solenoid HS-11 is open to
exhaust hydraulic fluid back to tank and travel brake is
spring-applied.
When travel brake switch is in off - park position, travel
command sends an input signal to the PC. The PC prepares
crane travel system for operation. Travel brakes remain
spring-applied until a travel handle or pedal is moved from
neutral position. When a travel handle or pedal is moved,
travel brake release solenoid HS-11 shifts to block tank port
and supplies hydraulic charge pressure from rear drum
pump to hydraulically release both spring brakes. If brake
pressure or electrical power is lost when operating, brakes
spring-apply.
Travel Forward and Reverse
Both right and left travel forward closed-loop systems
operate the same, except fluid flows from left travel pump
port A to left travel motor port A and from right travel pump
port A to right travel motor port B.
When left or right travel handle or pedal is moved in forward
direction, an input voltage of 5 volts or more is sent to the PC.
The PC sends a positive output signal to selected travel
pump EDC and enables travel brake release solenoid HS-11.
Travel brake release solenoid HS-11 shifts to release left and
right travel brake with charge pressure from rear drum pump,
before selected travel pump strokes.
Selected travel pump EDC tilts swashplate in forward
direction. Fluid flows from selected travel pump through
swivel to travel motor. The PC controls input voltage to
selected travel pump EDC, controlling travel speed relative
to selected travel handle or pedal movement.
When left or right travel handle or pedal is moved in reverse
direction, an input voltage of 5 volts or less is sent to the PC.
The PC sends a negative output signal to selected travel
pump EDC and enables travel brake release solenoid HS-11.
Travel brake release solenoid HS-11 shifts to release left and
right travel brake with charge pressure from rear drum pump,
before selected travel pump strokes.
Selected travel pump EDC tilts swashplate in reverse
direction. Fluid flows from selected travel pump through
swivel to travel motor. The PC controls input voltage to
selected travel pump EDC, controlling travel speed relative
to selected travel handle or pedal movement.
As left or right travel handle or pedal nears neutral position,
the PC compensates for hydraulic system leakage or
changing engine speed. The PC sends an output signal to
adjust swashplate to centered position. When travel handle
or pedal command is off for a preset time, the PC sends an
output signal to disable travel brake release solenoid HS-11.
Travel brake release solenoid valve shifts to block charge
pressure to brakes. This opens a line to tank for brake
hydraulic fluid and brakes spring-apply.
Travel Speed-High/Low Operation
Travel motors are variable displacement and shift internally
with an adjustable spring in each motor P/C (Pressure
Compensator) valve, preset at 3,915 psi (270 bar). Travel
speed switch (13) allows operator to select
LOW
when
smoother starts and precise control over the load is required
or high when maximum available travel speed is required.
When travel speed switch is in low position, the PC sends an
output signal to enable 2-speed travel solenoid HS-12,
shifting valve and directing pilot charge pressure to end of
the P/C valve. The P/C valve shifts PCOR spool placing
travel motor in maximum displacement (high torque, low
speed) position. Travel motors remain in this position until
travel speed switch is placed in high position and engine
speed is more than 1500 rpm.
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