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Service Manual
Series T90 Axial Piston Pumps
Operation
Manual OverRide (MOR)
16 |
©
Danfoss | March 2020
displacement in one direction to full displacement in the opposite direction. Under some circumstances,
such as contamination, the control spool could stick and cause the pump to stay at some displacement.
HCEDC schematic
M14
C
2
F00B
Feedback from
Swash plate
A serviceable 125 μm screen is located in the supply line immediately before the control porting spool.
HCEDC Operation
T90 HCEDC'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 equilibrium 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 HCEDC incorporates a positive neutral deadband as a result of the control spool porting, pre-loads
from the servo piston assembly, and the linear control spring. Once the neutral threshold current is
reached, the swashplate is positioned directly proportional to the control current. To minimize the effect
of the control neutral deadband, we recommend the transmission controller or operator input device
incorporate a jump up current to offset a portion of the neutral deadband.
The neutral position of the control spool does provide a positive pre-load pressure to each end of the
servo piston assembly.
When the control input signal is either lost or removed, or if there is a loss of charge pressure, the spring-
loaded servo piston will automatically return the pump to the neutral position.
All high current controls are standard with Manual Over Ride (MOR), used for temporary actuation of the
control to aid in diagnostics.
Unintended MOR operation will cause the pump to go into stroke. The vehicle or device must always be
in a safe condition (i.e. vehicle lifted off the ground) when using the MOR function. The MOR plunger has
a 4 mm diameter and must be manually depressed to be engaged. Depressing the plunger mechanically
moves the control spool which allows the pump to go on stroke. The MOR should be engaged
anticipating a full stroke response from the pump.
W
Warning
An O-ring seal is used to seal the MOR plunger where initial actuation of the function will require a force
of 45 N to engage the plunger. Additional actuations typically require less force to engage the MOR
plunger. Proportional control of the pump using the MOR should not be expected.
Refer to the control flow table for the relationship of solenoid to direction of flow.
C
1
F00A
T
P
P003 478E
AX216086485386en-000101
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