Manual Displacement Control (MDC)
MDC principle
An MDC is a Manual proportional Displacement Control (MDC).
The 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 swashplate rotation. The MDC changes the pump
displacement between no flow and full flow into opposite directions.
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.
MDC control
MDC schematic diagram
MDC operation
In difference to other controls the MDC spool provides a mechanical deadband. This is 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 internal end stop is not applicable for any limitation of the Bowden cable stroke, except the applied
torque to the shaft will never exceed 20 Nm. Customers must install some support to limit the setting
range of their Bowden cable.
The MDC provides a permanent restoring moment in direction to its neutral position. This is required to
take the backlash out of the mechanical connections between the Bowden cable and the control. The
restoring moment is appropriate turning the shaft back to neutral when the connection to the Bowden
cable is lost. It is not appropriate to force a Bowden cable or a joystick back to neutral!
Neutral Start Switch
MDC controls are available with neutral start schwitch (NSS). The Neutral Start Switch contains an
electrical switch that provides a signal of whether the control is in neutral. The signal in neutral is
normally closed (NC).
Basic Information
H1 Axial Piston Pumps, Single and Tandem
Operation
©
Danfoss | April 2017 11062168 | BC00000057en-US0602 | 11
To Next Page
Loading...
Need help?
General
