Manitowoc Grove RT770E, Service Maintenance Manual

Page: 181 / 357

4-37 Published 11/26/2014, Control # 447-05
RT770E SERVICE MANUAL BOOM
4
GROVE
TELESCOPE CIRCUIT
Description
The boom telescope circuit consists of the telescope
hydraulic remote controller, telescope directional control
valve, Telescope Stage Selector Valve, Telescope Fill Tube
Control Valve, holding valve, and the 2-stage telescope
cylinder.
NOTE: If the crane is equipped with an auxiliary hoist, the
telescope function is controlled by a foot pedal
instead of a controller.
Refer to Valves , page 2-30 for a complete description of the
hydraulic remote controller, the Telescope Stage Selector
Valve Manifold, and the Telescope Fill Tube Control Valve
Manifold.
Theory of Operation
The boom can be operated using several different modes.
The boom is operated in a synchronized sequence using a
two-stage telescope cylinder. Tele 1 is controlled by the
cylinder’s smaller piston and Tele 2 is controlled by the larger
piston. Tele 3 and 4 are controlled by cables fixed to Tele 2.
The cylinder is controlled using several proportionally control
solenoid operated valves.
Pressure in the telescope cylinder is monitored by two
pressure transducers, TR1 and TR2. TR1, also called the Fill
Tube Pressure Transducer, monitors the pressure in the
telescope cylinder fill tube. TR2, called the Small Piston
Pressure Transducer, monitors the pressure on the
telescope extend circuit. When Tele 2 is extended, TR1 and
TR2 monitor the same pressure. Both pressure transducers
communicate via CAN messages to the boom control
system. Pressure readings are monitored by the boom
c o n t r o l s y s t e m a n d a r e c o n t r o l l e d t o m a i n ta i n
synchronization of the boom in Auto and Manual Modes.
Boom Control Modes
The boom control offers four methods of telescoping the
boom: Auto Mode A, Auto Mode B, Manual Mode, and
Recovery Mode.
Auto A Mode
In the auto A mode, the boom extends to full length by
extending Tele 2 first then Tele 1. The crane decides how
and when to stop extending Tele 2 and start extending Tele
1. This mode is an option for normal crane work. The boom
control system uses length feedback to ramp the telescoping
speed of the boom sections when approaching the fully
retracted or fully extended positions, and near the transition
point. This mode has the best stability performance.
Auto B Mode
In the auto B mode, the boom extends to full length by
extending Tele 1 first then Tele 2. The crane decides how
and when to stop extending Tele 1 and start extending Tele
2. This mode is a second option for normal crane work. The
boom control system uses length feedback to ramp the
telescoping speed of the boom sections when approaching
the fully retracted or fully extended positions, and near the
transition point. This mode has the best structural
performance.
Manual Mode
In the manual mode, either Tele 1 or Tele 2 extends based on
the cab switch position. Once the selected section is
extended the operator must change the T1/T2 switch
position to extend the other section of the boom. This mode
may be used for lifting, but the load charts are substantially
reduce as compared to the Auto modes. Manual mode has
been designed for use in bringing the boom back into the
sequence of Auto Mode A or Auto Mode B. It is also useful
for lubrication or maintenance of the boom.
When the operator telescopes Tele 1, the boom control
system will maintain the relative position (percent extended)
of Tele 2, 3, and 4. When the operator telescopes Tele 2, 3,
and 4, the relative position of Tele 1 is maintained.
Manual mode does not ramp the speed of the boom near
transition points. The boom speed is controlled by the
operator.