Danfoss LDU20, LDU24 User guide
Technical Information
LDU20/24
Closed Circuit Axial Piston Transmission
www.danfoss.com
Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Revision history Table of revisions
Date Changed Rev
May 2021 Added Size 24 0301
January 2021 Minor update in Physical Properties 0208
December 2020 Minor correction 0207
Novemebr 2020 Minor update 0206
June 2020 Changed document number from 'BC00000192' and 'L1124546' to 'BC152886483777' 0205
April 2019 Fixed Control Handle Requirements 0103
April 2018 Minor update 0102
June 2016 Converted to New Danfoss layout 0101
December 2014 Converted to DITA CMS AD
March 2013 Paint and Tag AC
March 2011 2nd edition AB
January 2011 First edition AA
2 | © Danfoss | May 2021 BC152886483777en-000301
Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Contents
General description
Basic Design........................................................................................................................................................................................4
Key Features....................................................................................................................................................................................... 4
Typical Applications........................................................................................................................................................................ 4
Schematic diagram..........................................................................................................................................................................4
Technical Specification
Physical properties...........................................................................................................................................................................5
Operation Parameters.....................................................................................................................................................................5
Fluid Specifications..........................................................................................................................................................................6
Operations
Check / High Pressure Relief Valve ............................................................................................................................................7
Bypass Function................................................................................................................................................................................8
CPRV (Charge Pressure Relief Valve)..........................................................................................................................................9
Control............................................................................................................................................................................................... 10
Direct Displacement Control................................................................................................................................................10
Control Handle Requirements ............................................................................................................................................ 10
Operating Parameters
Overview........................................................................................................................................................................................... 11
Input Speed......................................................................................................................................................................................11
System Pressure..............................................................................................................................................................................11
Input Power......................................................................................................................................................................................11
Charge Pressure..............................................................................................................................................................................11
Case pressure...................................................................................................................................................................................12
Viscosity.............................................................................................................................................................................................12
Temperature.................................................................................................................................................................................... 12
System Design Parameters
Filtration System ............................................................................................................................................................................13
Filtration............................................................................................................................................................................................ 14
Charge Filtration....................................................................................................................................................................... 14
Suction Filtration.......................................................................................................................................................................14
Independent Braking System....................................................................................................................................................15
Fluid Selection.................................................................................................................................................................................15
Reservoir............................................................................................................................................................................................15
Case Drain.........................................................................................................................................................................................15
Charge Pump...................................................................................................................................................................................15
Bearing Loads and Life.................................................................................................................................................................16
Applications with External Shaft Loads............................................................................................................................16
Input Shaft...................................................................................................................................................................................17
Shaft Torque Rating and Spline Lubrication...................................................................................................................18
Shaft Availability and Torque Ratings...............................................................................................................................18
Sizing Equations............................................................................................................................................................................. 19
Model Code
Model Code: A - H.......................................................................................................................................................................... 20
Model Code: J - M...........................................................................................................................................................................21
Model Code: N - Z...........................................................................................................................................................................22
Installation Drawings
Shaft Availability and Torque Ratings: Input Shaft/PTO Shaft.......................................................................................23
Shaft Availability and Torque Ratings: Output Shaft........................................................................................................ 24
Installation Drawings LDU20/24...............................................................................................................................................25
Center section: Option A.............................................................................................................................................................27
Center section: Option B............................................................................................................................................................. 28
Center section: Option F..............................................................................................................................................................29
Center section: Option H.............................................................................................................................................................30
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MA1
MB1
MA2
MB2
L1
L2
L3
S
M3
P400004
Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
General description
Basic Design
LDU20/24 is a kind of U-style HST hardware, including a closed circuit variable displacement piston pump
with DDC (Direct displacement control) and a fixed motor. LDU20/24 is specially designed with optimized
performance, size, and cost, in order to fulfill the demand of the mobile applications marketplace. This
document provides the detailed specifications and features for LDU20/24.
Key Features
Easy to use design as Complete Hydrostatic Transmission package for Turf care machines & Compact
•
Utility Tractors up to 26 kw[35 PS]
Compact design
•
U-style layout in One housing with Z-shaft configuration
•
Require external charge
•
Bypass valve to allow the vehicle to be towed
•
Same shaft center distance as BDU21 85mm…Between pump and motor shaft
•
Same drive line design is available between BDU21 and LDU20/24
•
Best in class Efficiency by Female Piston & Male slipper design…Can reach approximately 80% overall
•
efficiency
Longer life kit, Higher Duty Cycle capability in the most compact design in this class of HST
•
Low trunnion operating force
•
Serviced by a Worldwide Network of Danfoss
•
Typical Applications
Schematic diagram
Compact utility tractor
•
Turf care
•
Small agricultural machinery
•
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Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Technical Specification
Physical properties
Features Units LDU20 LDU24
Displacement
Recommended charge pump displacement for external charge supply cm3/rev [in3/rev] 6 [0.37]
Torque at maximum displacement (theoretical)
Mass moment of inertia of
rotating components
Weight dry kg [lb] 14.1 [31.1]
Oil volume
Installation See Installation Drawings on page 25-30
Rotation Clockwise or Counterclockwise
Ports (ISO 11926-1) See Installation Drawings on page 25-30
Input shafts and PTO shafts See Installation Drawings on page 23
Output shaft See Installation Drawings on page 24
Control type DDC
1
Max Swash angle is 18 deg.
Pump side
Motor side 20 [1.22] 24 [1.46]
Pump side
Motor side 0.000928 [0.000683]
Case only
With passage 1.2 [0.32]
1
cm3/rev [in3/rev]
N•m/bar [lbf•in/1000 psi]
kg•m2 [slug•ft2]
liter [US gal]
0-20 [0-1.22] 0-24 [0-1.46]
0.32 [195.2] 0.38 [234.2]
0.000936 [0.000693]
1.1 [0.28]
Operation Parameters
Features Units LDU20 LDU24
Minimum for external charge supply
Input speed
System pressure
Input power Maximum kw [PS] 22 [30] 26 [35]
Charge pressure Minimum bar [psi] 5 [73]
Case pressure
Minimum for full performance 1300
Rated 3400
Maximum 3800
Maximum working pressure
Maximum pressure 345 [500]
Rated
Maximum 3 [43.5]
min-1 (rpm)
bar [psi]
bar [psi]
500
300 [4350]
1 [14.5]
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Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Technical Specification
Fluid Specifications
Features Units LDU20/24
Viscosity
Temperature
Filtration
(recommended minimum)
Minimum
Recommended range 12-60 [66-280]
Maximum 1600 [7500]
Minimum
Recommended range +82 [+180]
Maximum +104 [+220]
Cleanliness per ISO 4406 22/18/13
Efficiency (charge pressure filtration)
Efficiency (suction and return line
filtration)
Recommended inlet screen mesh
size
mm2/sec. [ SUS]
Degrees C [Degrees F]
β-ratio
µm 100-125
7 [49]
-40 [-40]
β15-20=75(β10≥10)
β15-20=75(β10≥10)
6 | © Danfoss | May 2021 BC152886483777en-000301
P400005
C
Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Operations
Check / High Pressure Relief Valve
LDU20/24 is equipped with a combination high pressure relief and charge check valve. The high-pressure
relief function is a dissipative (with heat generation) pressure control valve for the purpose of limiting
excessive system pressures. The charge check function acts to replenish the low-pressure side of the
working loop with charge oil. Each side of the transmission loop has a dedicated HPRV valve that is nonadjustable with a factory set pressure. When system pressure exceeds the factory setting of the valve, oil
is passed from the high pressure system loop, into the charge gallery, and into the low pressure system
loop via the charge check.
The order code allows for different pressure settings to be used at each system port. HPRV valve with
orifice is available to gain wider neutral dead-band. When HPRV valves with orifice are used, it is only for
High pressure ports when vehicle goes in reverse. The system pressure order code for transmissions with
only HPRV is a reflection of the HPRV setting.
The system pressure order code for transmissions configured with pressure limiter and HPRV is a
reflection of the pressure limiter setting.
Check/High pressure relief valve with orifice
As an option, LDU20/24 offers Check / HPRV with an orifice produce a larger neutral deadband.
In some applications, it is desirable to use Check / HPRV with an orifice to expand null dead band, which
would help provide a larger margin of safety for vehicle movement in neutral and provide easier
adjustment of the vehicle linkage for machine neutral. The orifice connects the working loop, which is a
main hydraulic circuit, to a charge circuit. It always allows some internal leakage to ensure the expanding
null dead band around neutral position of control shaft. However, it decreases the volumetric efficiency,
particularly at high system pressure in the working loop. Check / HPRV with an orifice has possibility to
increase downhill creap. It is recommended to install the orifice in a specific working loop, which is
pressurized when the vehicle moves in reverse.
The HPRV are set at the following flow rates
Check/HPRV without orifice 5 l/min [1.3 US gal/min]
Check/HPRV with orifice 17 l/min [4.5 US gal/min]
Caution
HPRV´s are factory set at a low flow condition. Any application or operating condition which leads to
elevated HPRV flow will cause a pressure rise with flow above a valve setting. Consult factory for
application review.
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System Pressure
Bypass Valve
System Pressure
P400006
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Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Operations
Bypass Function
The LDU20/24 contains a dedicated bypass valve option. The bypass function is activated when the
bypass valve is mechanically backed out 3 full turns (maximum). The bypass function allows a machine or
load to be moved without rotating the pump shaft or prime mover. In some applications, it is desirable to
bypass the fluid around the variable displacement pump when pump shaft rotation is unachievable or
undesired. To illustrate, an inoperable vehicle may need to be moved to the service or the repair location,
or winched onto a trailer without operating the prime mover. Thus, LDU20/24 is designed with the
bypass function as an option.
Bypass Function
Caution
Excessive speed or extended movement will damage the transmission.
Avoid excessive speeds and extended load/vehicle movement. Do not move the load or vehicle more
than 20 % of maximum speed or for longer than 3 minutes. When the bypass function is no longer
needed, reseat the bypass valve to the normal operating position.
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Charge Flow
P400007
Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Operations
CPRV (Charge Pressure Relief Valve)
The charge pressure relief valve maintains charge pressure at a designated level above case pressure. The
charge pressure relief valve is a direct acting poppet valve which opens and discharges fluid to the HST
case when pressure exceeds a designated level. For external charge flow the CPRV is set according to
below table. The charge pressure relief valve setting is specified on the model code of the transmission.
Charge Pressure Relief Valve settings for external charge supply
LDU 20/24 10.8 [2.9]
Charge Pressure Relief Valve Function
Flow l/min [US gal/min]
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Danfoss | May 2021 BC152886483777en-000301 | 9
W
Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Operations
Control
Direct Displacement Control
The LDU20/24 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.
The control input shaft is configurable on both of left and right hand side of the LDU20/24.
Control Handle Requirements
Maximum allowable trunnion torque is 79.1 N•m [700 lbf•in]. The approximate torque necessary to rotate
the control arm at 300 bar system operating pressure and 3000 rpm is 25 N•m with the standard
valveplate. Minimum torque necessary to hold the swashplate at a zero angle for neutral is 2.3 N•m [20
in•lbf ]. The actual value will vary due to the influence of pump operating conditions. For mating
dimensions, see Installation Drawings LDU20/24 on page 25.
Input shaft rotation CW CCW
Trunnion location Right Left Right Left
Trunnion rotation CW CCW CW CCW CW CCW CW CCW
Output rotation CCW CW CW CCW CW CCW CCW CW
High pressure port MA MB MB MA MB MA MA MB
Low pressure port MB MA MA MB MA MB MB MA
Warning
With no external forces applied to the swashplate trunnion, internal hydraulic forces may not return the
swashplate to the neutral position under all conditions of operation.
10 | © Danfoss | May 2021 BC152886483777en-000301
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