Manual Displacement Control (Mdc); Mdc Operation - Danfoss H1P 045 Service Manual

Service Manual
H1P 045/053/060/068 Axial Piston Single Pumps
Operation

Manual Displacement Control (MDC)

18 | © Danfoss | June 2020
A Manual proportional Displacement Control (MDC) consists of a handle on top of a rotary input shaft.
The shaft provides an eccentric connection to a feedback link. This link is connected on its one end with a
porting spool. On its other end the link is connected the pumps swashplate.
This design provides a travel feedback without spring. When turning the shaft the spool moves thus
providing hydraulic pressure to either side of a double acting servo piston of the pump.
Differential pressure across the servo piston rotates the swash plate, changing the pump's displacement.
Simultaneously the swashplate movement is fed back to the control spool providing proportionality
between shaft rotation on the control and swash-plate rotation. The MDC changes the pump
displacement between no flow and full flow into opposite directions.
Under some circumstances, such as contamination, the control spool could stick and cause the pump to
stay at some displacement.
For the MDC with CCO option the brake port (X7) provides charge pressure when the coil is energized to
activate static function such as a brake release. The X7 port must not be used for any continuous oil
consumption.
The MDC is sealed by means of a static O-ring between the actuation system and the control block. Its
shaft is sealed by means of a special O-ring which is applied for low friction. The special O-ring is
protected from dust, water and aggressive liquids or gases by means of a special lip seal.
Manual Displacement Control

MDC Operation

The MDC provides a mechanical dead-band required to overcome the tolerances in the mechanical
actuation. The MDC contains an internal end stop to prevent turning the handle into any inappropriate
position.
The MDC provides a permanent restoring moment appropriate for turning the MDC input shaft back to
neutral position only. This is required to take the backlash out of the mechanical connections between
the Bowden cable and the control.
C
Caution
High case pressure may cause excessive wear and the NSS to indicate that the control is not in neutral
position. In addition, if the case pressure exceeds 5 bar there is a risk of an insufficient restoring moment.
The MDC is designed for a maximum case pressure of 5 bar and a rated case pressure of 3 bar.
Pump displacement vs. control lever rotation
100 %
-d -b
-a
Lever rotation
"A"
"0"
-c a
100 %
Deadband on B side: a = 3° ±1°
Maximum pump stroke: b = 30° +2/-1°
Required customer end stop: c = 36° ±3°
Internal end stop: d = 40°
d
"B"
b c
P301 752
AX152886481964en-000405