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 |
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Date |
Changed |
Rev |
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May 2021 |
Added Size 24 |
0301 |
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January 2021 |
Minor update in Physical Properties |
0208 |
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December 2020 |
Minor correction |
0207 |
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Novemebr 2020 |
Minor update |
0206 |
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June 2020 |
Changed document number from 'BC00000192' and 'L1124546' to 'BC152886483777' |
0205 |
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April 2019 |
Fixed Control Handle Requirements |
0103 |
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April 2018 |
Minor update |
0102 |
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June 2016 |
Converted to New Danfoss layout |
0101 |
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December 2014 |
Converted to DITA CMS |
AD |
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March 2013 |
Paint and Tag |
AC |
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March 2011 |
2nd edition |
AB |
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January 2011 |
First edition |
AA |
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2 | © Danfoss | May 2021 |
BC152886483777en-000301 |
Technical Information |
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LDU20/24 Closed Circuit Axial Piston Transmission |
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Contents |
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General description |
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Basic Design........................................................................................................................................................................................ |
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Key Features....................................................................................................................................................................................... |
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Typical Applications........................................................................................................................................................................ |
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Schematic diagram.......................................................................................................................................................................... |
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Technical Specification |
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Physical properties........................................................................................................................................................................... |
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Operation Parameters..................................................................................................................................................................... |
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Fluid Specifications.......................................................................................................................................................................... |
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Operations |
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Check / High Pressure Relief Valve ............................................................................................................................................ |
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Bypass Function................................................................................................................................................................................ |
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CPRV (Charge Pressure Relief Valve).......................................................................................................................................... |
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Control............................................................................................................................................................................................... |
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Direct Displacement Control................................................................................................................................................ |
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Control Handle Requirements ............................................................................................................................................ |
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Operating Parameters |
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Overview........................................................................................................................................................................................... |
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Input Speed...................................................................................................................................................................................... |
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System Pressure.............................................................................................................................................................................. |
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Input Power...................................................................................................................................................................................... |
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Charge Pressure.............................................................................................................................................................................. |
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Case pressure................................................................................................................................................................................... |
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Viscosity............................................................................................................................................................................................. |
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Temperature.................................................................................................................................................................................... |
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System Design Parameters |
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Filtration System ............................................................................................................................................................................ |
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Filtration............................................................................................................................................................................................ |
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Charge Filtration....................................................................................................................................................................... |
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Suction Filtration....................................................................................................................................................................... |
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Independent Braking System.................................................................................................................................................... |
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Fluid Selection................................................................................................................................................................................. |
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Reservoir............................................................................................................................................................................................ |
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Case Drain......................................................................................................................................................................................... |
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Charge Pump................................................................................................................................................................................... |
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Bearing Loads and Life................................................................................................................................................................. |
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Applications with External Shaft Loads............................................................................................................................ |
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Input Shaft................................................................................................................................................................................... |
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Shaft Torque Rating and Spline Lubrication................................................................................................................... |
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Shaft Availability and Torque Ratings............................................................................................................................... |
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Sizing Equations............................................................................................................................................................................. |
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Model Code |
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Model Code: A - H.......................................................................................................................................................................... |
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Model Code: J - M........................................................................................................................................................................... |
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Model Code: N - Z........................................................................................................................................................................... |
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Installation Drawings |
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Shaft Availability and Torque Ratings: Input Shaft/PTO Shaft....................................................................................... |
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Shaft Availability and Torque Ratings: Output Shaft........................................................................................................ |
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Installation Drawings LDU20/24............................................................................................................................................... |
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Center section: Option A............................................................................................................................................................. |
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Center section: Option B............................................................................................................................................................. |
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Center section: Option F.............................................................................................................................................................. |
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Center section: Option H............................................................................................................................................................. |
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© Danfoss | May 2021 |
BC152886483777en-000301 | 3 |
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
•Compact utility tractor
•Turf care
•Small agricultural machinery
Schematic diagram
L3 |
S |
M3 |
MA1 |
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MA2 |
MB1 |
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MB2 |
L1 |
L2 |
P400004 |
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4 | © Danfoss | May 2021 |
BC152886483777en-000301 |
Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Technical Specification
Physical properties
Features |
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Units |
LDU20 |
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LDU24 |
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Displacement |
Pump side1 |
cm3/rev [in3/rev] |
0-20 [0-1.22] |
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0-24 [0-1.46] |
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Motor side |
20 [1.22] |
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24 [1.46] |
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Recommended charge pump displacement for external charge supply |
cm3/rev [in3/rev] |
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6 [0.37] |
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Torque at maximum displacement (theoretical) |
N•m/bar [lbf•in/1000 psi] |
0.32 [195.2] |
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0.38 [234.2] |
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Mass moment of inertia of |
Pump side |
kg•m2 [slug•ft2] |
0.000936 [0.000693] |
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rotating components |
Motor side |
0.000928 [0.000683] |
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Weight dry |
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kg [lb] |
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14.1 [31.1] |
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Oil volume |
Case only |
liter [US gal] |
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1.1 [0.28] |
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With passage |
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1.2 [0.32] |
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Installation |
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See Installation Drawings on page 25-30 |
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Rotation |
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Clockwise or Counterclockwise |
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Ports (ISO 11926-1) |
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See Installation Drawings on page 25-30 |
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Input shafts and PTO shafts |
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See Installation Drawings on page 23 |
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Output shaft |
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See Installation Drawings on page 24 |
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Control type |
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DDC |
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1 Max Swash angle is 18 deg. |
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Operation Parameters
Features |
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LDU20 |
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LDU24 |
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Minimum for external charge supply |
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500 |
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Input speed |
Minimum for full performance |
min-1 (rpm) |
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1300 |
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Rated |
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3400 |
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Maximum |
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3800 |
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System pressure |
Maximum working pressure |
bar [psi] |
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300 [4350] |
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Maximum pressure |
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345 [500] |
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Input power |
Maximum |
kw [PS] |
22 [30] |
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26 [35] |
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Charge pressure |
Minimum |
bar [psi] |
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5 [73] |
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Case pressure |
Rated |
bar [psi] |
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1 [14.5] |
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Maximum |
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3 [43.5] |
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© Danfoss | May 2021 |
BC152886483777en-000301 | 5 |
Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Technical Specification
Fluid Specifications
Features |
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Units |
LDU20/24 |
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Minimum |
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7 [49] |
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mm2/sec. [ SUS] |
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Viscosity |
Recommended range |
12-60 [66-280] |
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Maximum |
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1600 [7500] |
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Minimum |
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-40 [-40] |
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Temperature |
Recommended range |
Degrees C [Degrees F] |
+82 [+180] |
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Maximum |
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+104 [+220] |
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Cleanliness per ISO 4406 |
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22/18/13 |
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Efficiency (charge pressure filtration) |
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β15-20=75(β10≥10) |
Filtration |
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β-ratio |
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Efficiency (suction and return line |
β15-20=75(β10≥10) |
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(recommended minimum) |
filtration) |
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Recommended inlet screen mesh |
µm |
100-125 |
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size |
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6 | © Danfoss | May 2021 |
BC152886483777en-000301 |
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] |
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Check/HPRV with orifice |
17 l/min [4.5 US gal/min] |
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P400005
C 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.
© Danfoss | May 2021 |
BC152886483777en-000301 | 7 |
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
Bypass Valve
System Pressure |
System Pressure |
P400006
C 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.
8 | © Danfoss | May 2021 |
BC152886483777en-000301 |
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
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Flow l/min [US gal/min] |
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LDU 20/24 |
10.8 [2.9] |
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Charge Pressure Relief Valve Function
Charge Flow
P400007
© Danfoss | May 2021 |
BC152886483777en-000301 | 9 |
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 |
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CW |
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CCW |
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Trunnion location |
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Right |
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Left |
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Right |
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Left |
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Trunnion rotation |
CW |
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CCW |
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CW |
CCW |
CW |
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CCW |
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CW |
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CCW |
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Output rotation |
CCW |
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CW |
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CW |
CCW |
CW |
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CCW |
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CCW |
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CW |
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High pressure port |
MA |
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MB |
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MB |
MA |
MB |
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MA |
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MA |
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MB |
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Low pressure port |
MB |
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MA |
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MA |
MB |
MA |
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MB |
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MB |
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MA |
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W 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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