HOISTS MLC300 SERVICE/MAINTENANCE MANUAL
5-16
Published 11-22-17, Control # 257-02
Neutral
When drum 4 joystick J1 is moved back to neutral, the pump
swashplate shifts to neutral, stopping hydraulic flow in the
open-loop circuit.
The motor swashplate will then go to minimum
displacement, and the drum 4 brake release solenoid valve
(14) de-energizes, opening a return path to the tank. The
brake pressure vents to the tank via the brake defeat valve
(22) and the brake release solenoid valve, allowing spring
force to apply the drum brake (17).
When in neutral, the load-holding valve (12) closes to block
oil flow from the hydraulic motor (18).
If hydraulic pressure is lost on the low-pressure side of the
hydraulic motor during operation, the brake defeat valve
closes, venting the drum brake pressure directly to the tank.
This allows the drum brake to immediately apply to stop the
drum.
Drum 4 Lowering Operation
The following conditions must be met to operate drum 4:
• Seat safety switch must be closed
• Drum 4 must be un-parked
When the drum 4 joystick J1 is pushed forward to lower the
boom, the CCM-10 control module sends an electrical signal
to the drum 4 system A control valve (8), and the CCMC11
control module sends an electrical signal to the drum 4
system B control valve (9). The control valves shift to a
position that routes hydraulic fluid to the lower hoist side of
the system.
The CCM-10 control module then sends a pulse-width
modulated (PWM) signal to the electronic displacement
controls (EDC) on pumps 3 and 4 (3 and 4). The PWM signal
is in proportion to the speed commanded by the joystick.
Increasing the PWM duty cycle increases the pumps’
swashplate angle, which increases the hydraulic flow from
the pumps through the A ports of the system A and system B
control valves (8 and 9), then to the sequence valve (25) on
the A side of the hydraulic motor (18).
The oil flows through the check valve in the sequence valve
to the A port of the hydraulic motor, causing the motor to
attempt to turn the drum.
At the same time, the IOLC31 control module sends 24 V
DC
to the brake release solenoid valve (14), energizing the
solenoid. The brake valve shifts to a position that routes
hydraulic fluid from the pump 1 charge pump (6) to the brake
defeat valve (22). Hydraulic pressure on the A side of the
motor shifts the brake defeat valve. This allows the hydraulic
fluid from the brake release solenoid valve to flow to the
drum brake (17), releasing the brake.
As the motor starts to rotate, hydraulic pressure on the B
side of the motor shifts the load holding-valve (12) to the
open position, which meters the return hydraulic fluid as it
flows back to the tank via the drum 4 system A and system B
control valves. This allows the drum to turn in the direction
that lowers the boom.
The CCM-10 control module then sends a signal to the
IOLC31 control module via the CAN Bus to ramp up the
PWM duty cycle to the drum 4 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 following sensors provide feedback to the controllers:
• Drum 4 Motor Speed Sensor
• Pump 3 Pressure Transducer
(pump 3 system B psi)
• Pump 4 Pressure Transducer
(pump 4 system A psi)
• Drum 4 Motor Pressure Transducer
(drum 4 motor psi)
• Drum 4 System A Pressure Transducer
(system A manifold psi)
• Drum 4 System B Pressure Transducer
(system B manifold psi)
The control system uses this feedback to adjust the pump
and motor flow to maintain the speeds commanded by drum
4 joystick J1.
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