INTRODUCTION 777 SERVICE MANUAL
1-66 Published 10-01-2012, Control # 045-08
stroke the pump in the up direction. Oil then flows from pump
port A to port A of auxiliary hoist motor.
Auxiliary hoist pressure sender supplies the PC with
pressure information, which the PC compares to the
memorized holding pressure of the auxiliary hoist. When
adequate pressure is available, the PC energizes HS9 to
shift the brake valve. This initiates full release of park brake
and auxiliary hoist motor raises the load.
The PC governs the raising speed of the load by varying the
voltage to the pump (up) EDC in proportion to movement of
the control handle. The angle of the pump swashplate is
increased as the control handle is moved farther backward,
pumping more oil to the motor and raising the load faster.
As control handle approaches the full handle command
position, and if lifting conditions permit, the PC instructs the
auxiliary hoist motor PCP valve to shift in proportion to
handle position and redirect oil flow to motor servo cylinder.
This allows the servo mechanism to shift the motor gradually
toward to minimum displacement for maximum motor speed
at less operating torque.
As control handle returns to the off position, the PC
commands the auxiliary hoist pump (up) EDC to decrease
the angle of the pump swashplate, causing a reduction in oil
flow output. The PC also instructs the auxiliary hoist motor
PCP valve to shift in proportion to handle position, the
auxiliary hoist motor to maximum displacement for slower
output speed to slow the drum rotation. When the control
handle is fully off, the PC memorizes the pressure required to
support the load and de-energizes HS9 to apply the brake
after the control handle neutral switch opens or after
receiving a zero command from drum speed sender.
Auxiliary Hoist Lower
See Figures 1-48 and 1-49 for following procedures.
When control handle is pushed forward for down operation,
the handle neutral switch closes, completing a regulated
voltage circuit from the handle potentiometer to the PC. The
PC interprets the signal for speed and direction and closes
regulated voltage circuits to the auxiliary hoist pump (down)
EDC, auxiliary hoist motor PCP, and auxiliary drum park
brake hydraulic solenoid HS9. These circuits will close only if
the seat switch is closed, if the auxiliary drum park switch is
off, the auxiliary drum pawl switch is disengaged, applicable
operating limit switches are closed, and no system or
operating faults are present.
Before the auxiliary drum brake is released, the PC supplies
regulated voltage to the auxiliary pump (up) EDC. The PC
programming requires auxiliary hoist pump to stroke
momentarily in the hoisting direction to ensure adequate
pressure is present to hold the load after full release of the
brake.
FIGURE 1-48
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