Control; Direct Displacement Control; Control Handle Requirements - Danfoss LDT 21 Service Manual

Service Manual
LDT 21/24/32 Closed Circuit Axial Piston Transmission
Operations

Control

© Danfoss | June 2022

Direct Displacement Control

The LDT21/24/32 features direct displacement control (DDC).The swashplate angle is set directly by a
control lever or linkage attached directly to the swashplate trunnion. Control lever movement changes
the speed and rotating direction of the motor by increasing or decreasing the swashplate angle.
LDT Control Handle Requirements
The minimum torque necessary to hold the swashplate at a zero angle will vary due to the influence of
pump operating conditions.
The control handle linkage / design provided by the customer is required to provide maximum angle
stops and should not rely on the internal hard stops in the LDT. This applies to both directions of the
trunnion rotation.
The LDT24 features two threaded (M10) holes near the trunnion. Contact Danfoss for proper application
guidelines if these holes are intended to be used for a neutral return mechanism.
Control Moments / Deadband
Stroke decreasing moment at max working system pressure, full
stroke, 2500 RPM input speed, 30 mm
Minimum return spring force at neutral, N·m [lbf·in]
Neutral deadband, 3000 RPM, no load, 30 mm
Neutral deadband, 3000 RPM, no load, 30 mm
orifice
Input shaft rotation (as seen from input shaft)
Trunnion location (as seen from input shaft)
Output Shaft Rotation (as seen from output shaft)
Control Shaft Rotation (as seen from control shaft)
High Pressure Port
Low Pressure Port
W
Warning
Neutral return mechanism (not supplied with the product) must be able to overcome on-stroking
moments at any operating condition.
W
Warning
With no external forces applied to the swashplate trunnion, internal hydraulic forces will not return the
swashplate to the neutral position under all conditions of operation.
LDT21
8.6 [76]
2
/sec. N·m [lbf·in]
10 [89]
2
/sec, with orifice 0.5°
2
/sec, without 1°
CW
Left
CW
CW(b)
MB
MA
LDT24 LDT32
20 [177] 20 [177]
10 [89] 18 [160]
0.5° 0.5°
1° 1°
CCW
CCW(a)
MA
MB
AX417167456877en-000101 | 11