INTRODUCTION 2250 SERVICE/MAINTENANCE MANUAL
1-42
Published 11-06-15, Control # 040-13
Travel System Operation
General
See Figure 1-23 and Figure 1-24 for the following procedure.
Each travel hydraulic pump drives one crawler system motor
and gearbox. Each hydraulic pump and motor is controlled
with travel control handle movement and the PC. Travel
control handles are inoperable when travel brake is applied.
Gearbox for each crawler is driven with a flexible shaft
connected between motor output and drive gearbox input.
To ensure that crane travels in a straight line forward or
reverse direction, each travel drive system has shuttle valves
and pressure senders that monitor hydraulic pressure to
each closed-loop system. When traveling, the PC monitors
information from pressure senders and adjusts displacement
of travel pumps to maintain equal pressure in each travel
drive system. This allows crane to track in a controlled
straight direction.
The source hydraulic pressure for releasing the travel brakes
and enabling motor servo systems is pilot pressure from
boom hoist charge pump at 350 psi (24 bar). Continuous
changing of closed-loop fluid occurs through leakage in
pump, motor, and loop flushing valves that removes 3
gallons per minute (11 L/min) of fluid to when system
pressure is above 350-psi (24 bar).
When either travel control handle is moved from off, an input
signal is sent to the PC. The PC sends a 12 volt output signal
to enable the optional swing/travel alarm. When travel
control handle is moved to off, the PC sends a 0 volt output
signal to disable the swing/travel alarm.
Travel Brakes
Hydraulic pressure required for releasing the travel brakes is
pilot pressure from boom hoist charge pump at 350 psi (24
bar). For travel brake operation the system pressure must be
above 200 psi (14 bar) for travel brakes to fully release from
each travel motor shaft. If system pressure is below 200-psi
(14 bar), travel brake could be partially applied and damage
the brake. If brake pressure or electrical power is lost when
operating, the travel brake is applied.
When travel brake switch is in on position, right and left travel
brakes are applied to hold crane in position. Travel brake
solenoid valve HS-1 is open to allow hydraulic flow from the
brake to tank.
When travel brake switch is in off position, an input signal is
sent to the PC. Travel system circuit is active, waiting for a
travel control handle command. When travel control handle
is moved the PC sends a 12 volt output to enable travel
brake solenoid valve HS-1. Brake solenoid valve shifts to
block tank port and supplies hydraulic charge pressure fluid
from boom hoist charge pump to hydraulically release both
crawler brakes. If brake pressure or electrical power is lost
when operating, brakes apply.
Two-Speed Travel Operation
Travel 2-speed switch allows operator to select low speed
when smoother start is required. Low speed places travel
motor in maximum displacement (high torque, low speed)
position and prevents motor from shifting to high speed.
Hydraulic pressure for releasing travel 2-speed solenoid
valve HS-35 is pilot pressure from boom hoist charge pump
at 350 psi (24 bar).
When travel speed switch is in low speed position, the PC
sends a 12 volt output to enable 2-speed travel solenoid
valve HS-35, shifting valve to direct hydraulic pilot pressure
to end of P/C valve. The P/C valve shifts PCOR (Pressure
Compensated Over-Ride) 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 speed position.
Place travel speed switch in high speed when maximum
available travel speed is required (normal operation). In high
speed position, travel motors shift to minimum displacement
(low torque, high speed) automatically if system pressure is
below 3,915 psi (270 bar). If engine is below 1500 RPM, 2-
speed travel solenoid valve HS-35 is enabled although travel
speed switch in the high position. Travel two-speed solenoid
valve HS-35 is disabled, shifting valve and removing
hydraulic pilot pressure to end of P/C valve, allowing motor
to operate in PCOR mode.
Travel Detent Selector
Travel detent selector on right travel control handle allows
any travel command to be locked-in. When moving at
desired speed and direction, lift travel detent selector on right
handle dome, the PC locks-in the information. Lifting travel
detent selector again or moving either travel control handle
in the opposite direction opens travel detent circuit and
returns control of travel system to the operator.
Travel Forward and Reverse
Both travel closed-loop systems operate the same, except
fluid flow to motor ports is different to each track.
When a travel control handle is moved in forward direction,
an input voltage of 5 or more volts is sent to The PC. The PC
sends a variable minus 0 to 2.8 volt output that is applied to
selected travel pump EDC. Travel brake solenoid valve HS-1
is enabled to release both left and right crawler brakes,
before selected travel pump(s) strokes.
Travel pump EDC tilts pump swashplate in the forward
direction. Hydraulic fluid flow is from pump port of selected
travel pump through quick disconnect and swivel to travel
motor. The PC input voltage to selected travel pump EDC
that is relative to selected control handle movement.
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