Electrical displacement control (edc), Electrical displacement control (edc) -37 – JLG 340AJ Service Manual User Manual
Page 195
SECTION 5 - HYDRAULICS
3121259
– JLG Lift –
5-37
Electrical Displacement Control (EDC)
EDC PRINCIPLE
The Electrical Displacement Control (EDC) consists of propor-
tional solenoids on each side of a three-position, four-way
porting spool. The proportional solenoid applies a force to the
spool, which ports hydraulic fluid to either side of the servo
piston. Differential pressure across the servo piston rotates the
swashplate, changing the pump's displacement from full dis-
placement in one direction to full displacement in the oppo-
site direction.
EDC OPERATION
H1 EDC's are current driven controls requiring a Pulse Width
Modulated (PWM) signal. Pulse width modulation allows more
precise control of current to the solenoids. The PWM signal
causes the solenoid pin to push against the porting spool,
which pressurizes one end of the servo piston, while draining
the other. Pressure differential across the servo piston moves
the swashplate. A swashplate feedback link, opposing control
links, and a linear spring provide swashplate position force
feedback to the solenoid. The control system reaches equilib-
rium when the position of the swashplate spring feedback
force exactly balances the input command solenoid force from
the operator. As hydraulic pressures in the operating loop
change with load, the control assembly and servo/swashplate
system work constantly to maintain the commanded position
of the swashplate.
The EDC incorporates a positive neutral dead-band as a result
of the control spool porting, spring preload from the servo pis-
ton assembly, and the linear control spring. Once the neutral
threshold current is reached, the swashplate position becomes
directly proportional to the control current.To minimize the
effect of the control neutral deadband, we recommended the
transmission controller or operator input device incorporate a
jump up current.
NOTE:
The neutral position of the control spool does provide a
positive preload pressure to each end of the servo piston
assembly.