Manitowoc Published 11-22-17, Control # 257-02 5-3
MLC300 SERVICE/MAINTENANCE MANUAL HOISTS
When the drum 1/3 selector solenoid valve is de-energized,
the following occurs:
• The drum 1/3 selector solenoid valve routes hydraulic
fluid from pump 2 to the drum 1 pilot control of the single
and double drum 1/3 diverter valves, causing these
valves to shift to the drum 1 position.
• With the drum 1/3 double diverter valve shifted to the
drum 1 position, hydraulic fluid from the main pump of
pump 2 is routed to the drum 1 motor. Return flow from
the motor is routed back to the pump via the double
diverter valve.
• With the drum 1/3 single diverter valve shifted to the
drum 1 position, the single diverter valve routes
hydraulic fluid from the charge pump of pump 2 to the
makeup check valve for motor anti-cavitation purposes.
Drum 1 Hoisting Operation
The following conditions must be met to operate drum 1:
• Seat safety switch must be closed
• Drum 3 must be parked
• Drum 1 must be un-parked
When drum 1 joystick J3 is pulled back to hoist a load, CCM-
10 control module sends a pulse-width modulated (PWM)
signal to the pump 2 electronic displacement control (EDC).
The PWM signal is in proportion to the speed commanded by
the joystick. Increasing the PWM duty cycle increases the
pump swashplate angle, which increases the hydraulic flow
from the B-side of the pump. From the pump, hydraulic flow
is routed through the drum 1/3 diverter valve, to the B-side of
the drum 1 motor.
At the same time, the IOLC32 control module shifts the drum
1 brake release valve, allowing hydraulic fluid to flow through
the valve to the brake cylinder, releasing the drum brake.
The CCM-10 control module then sends a signal to the
IOLC32 control module via the CAN Bus to ramp up the
PWM duty cycle to the drum 1 motor controller. Increasing
the PWM duty cycle decreases the swashplate angle in the
motor, which increases the motor flow until the rotational
speed is maximized based on the pump flow.
The drum 1 motor speed sensor and the pump 2 pressure
transducer provide closed-loop feedback to the controllers.
The control system uses this feedback to adjust the pump
and motor flow to maintain the speeds commanded by the
joystick.
Neutral
When drum 1 joystick J3 is moved back to neutral, the pump
swashplate shifts to neutral, stopping hydraulic flow in the
closed-loop circuit. The motor swashplate then shifts to
maximum displacement, and the drum 1 brake release
solenoid valve is de-energized. The de-energized solenoid
valve vents hydraulic brake pressure back to the tank,
allowing spring force to apply the drum brake.
Drum 1 Lowering Operation
The following conditions must be met to operate drum 1:
• Seat safety switch must be closed
• Drum 3 must be parked
• Drum 1 must be un-parked
When drum 1 joystick J3 is pushed forward to lower a load,
the CCM-10 control module sends a pulse-width modulated
(PWM) signal to the pump 2 electronic displacement control
(EDC). The PWM signal is in proportion to the speed
commanded by the joystick. Increasing the PWM duty cycle
increases the pump swashplate angle, which increases the
hydraulic flow from the A-side of the pump. From the pump,
hydraulic flow is routed through the drum 1/3 diverter valve to
the A-side of the drum 1 motor.
At the same time, the IOLC32 control module shifts the drum
1 brake release valve, allowing hydraulic fluid to flow through
the valve to the brake cylinder, releasing the drum brake.
The CCM-10 control module then sends a signal to the
IOLC32 control module via the CAN Bus to ramp up the
PWM duty cycle to the drum 1 motor controller. Increasing
the PWM duty cycle decreases the swashplate angle in the
motor, which increases the motor flow until the rotational
speed is maximized based on the pump flow.
The drum 1 motor speed sensor and the pump 2 pressure
transducer provide closed-loop feedback to the controllers.
The control system uses this feedback to adjust the pump
and motor flow to maintain the speeds commanded by the
joystick.
When needed, the makeup check valve opens to allow
charge pressure fluid to enter the low pressure side of the
loop, thereby maintaining a positive pressure at the motor
port.
Drum 1 Loop Flushing
Loop flushing (cooling) is achieved by the continuous
exchange of hydraulic fluid through the loop flushing valve.
When the drum is operated in either direction, the sequence
valve opens at 21 bar (300 psi), allowing hydraulic fluid from
the loop to flow through the normally open poppet valve to
the flow control valve. The flow control valve removes
approximately 38 L/min (10 gpm) of hot hydraulic fluid from
the system by discharging the exhausted hydraulic fluid into
the motor case where the hydraulic fluid returns to the tank.
The accumulator in the loop flushing circuit protects the drum
motor from damage due to thermal expansion during boom
butt storage/transport. If the pressure in the motor increases,
the pressure is captured in the accumulator.
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