Danfoss LDU20, LDU24 Service guide

Service Manual

LDU20/24

Closed Circuit Axial Piston Transmission

www.danfoss.com

Service Manual

LDU20/24 Closed Circuit Axial Piston Transmission

Revision history	Table of revisions
	Date	Changed	Rev
	June 2021	Added Size 24, Changed document number from 'AX00000049' and '11071687' to	0304
		'AX152886481311'
	July 2017	Updated to Engineering Tomorrow	0202
	March 2014	Danfoss layout	BA
	January 2011	First edition	AA

2 | © Danfoss | June 2021

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Service Manual
LDU20/24 Closed Circuit Axial Piston Transmission
Contents
Introduction
Overview..............................................................................................................................................................................................	5
Warranty..............................................................................................................................................................................................	5
General Instructions........................................................................................................................................................................	5
Remove the unit..........................................................................................................................................................................	5
Keep it clean..................................................................................................................................................................................	5
Lubricate moving parts.............................................................................................................................................................	5
Replace all O-rings and gaskets.............................................................................................................................................	5
Secure the unit.............................................................................................................................................................................	6
Safety Precautions............................................................................................................................................................................	6
Unintended machine movement..........................................................................................................................................	6
Flammable cleaning solvents.................................................................................................................................................	6
Fluid under pressure..................................................................................................................................................................	6
Personal safety.............................................................................................................................................................................	6
Hazardous material....................................................................................................................................................................	6
Symbols Used in Danfoss Literature..........................................................................................................................................	7
General Description
Basic Design........................................................................................................................................................................................	8
Key Features.......................................................................................................................................................................................	8
Typical Applications........................................................................................................................................................................	8
Schematic Diagram..........................................................................................................................................................................	8
Operation
HPRV (High Pressure Relief Valve) .............................................................................................................................................	9
Charge Check Relief Valve with Orifice...............................................................................................................................	9
Bypass Function..............................................................................................................................................................................	10
CPRV (Charge Pressure Relief Valve).......................................................................................................................................	11
Control...............................................................................................................................................................................................	11
Direct Displacement Control................................................................................................................................................	11
Control Handle Requirements.............................................................................................................................................	11
Operating Parameters
Overview...........................................................................................................................................................................................	12
Input Speed......................................................................................................................................................................................	12
System Pressure..............................................................................................................................................................................	12
Input Power......................................................................................................................................................................................	12
Charge Pressure..............................................................................................................................................................................	13
Case Pressure...................................................................................................................................................................................	13
Viscosity.............................................................................................................................................................................................	13
Temperature....................................................................................................................................................................................	13
Technical Specifications
General Specifications..................................................................................................................................................................	14
Physical Properties.........................................................................................................................................................................	14
Operating Parameters..................................................................................................................................................................	14
Fluid Specifications.......................................................................................................................................................................	15
Fluid and Filter Maintenance
Fluid and Filter Recommendations.........................................................................................................................................	16
Pressure Measurements
Port Locations and Gauge Installation...................................................................................................................................	17
Initial Startup Procedure
Startup Procedure..........................................................................................................................................................................	18
Troubleshooting
Overview...........................................................................................................................................................................................	19
System Operating Hot..................................................................................................................................................................	19
Transmission Operates Normally in One Direction Only.................................................................................................	19
System will not Operate in Either Direction.........................................................................................................................	19
System Noise or Vibration...........................................................................................................................................................	20
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Service Manual
LDU20/24 Closed Circuit Axial Piston Transmission
Contents
Sluggish System Response.........................................................................................................................................................	20
Required Tools and Standard Procedures
Required Tools................................................................................................................................................................................	21
Standard Procedures....................................................................................................................................................................	21
Charge Check/HPRV Adjustments...........................................................................................................................................	21
Checking for proper charge check/HPRV operation....................................................................................................	21
Minor Repair
Shaft Seals.........................................................................................................................................................................................	22
Removal........................................................................................................................................................................................	22
Inspection....................................................................................................................................................................................	22
Assembly......................................................................................................................................................................................	22
Charge Check/HPRV......................................................................................................................................................................	23
Removal........................................................................................................................................................................................	23
Inspection....................................................................................................................................................................................	23
Reassembly.................................................................................................................................................................................	23
Bypass Valve.....................................................................................................................................................................................	24
Removal........................................................................................................................................................................................	24
Inspection....................................................................................................................................................................................	24
Reassembly.................................................................................................................................................................................	24
Torque Chart
Plug Size and Torque Chart........................................................................................................................................................	25

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Service Manual

LDU20/24 Closed Circuit Axial Piston Transmission

Introduction

Overview

This manual includes information on the installation, maintenance, and minor repair of LDU20/24 transmission (HST). It includes a description of the unit and its individual components, troubleshooting information, and minor repair procedures.

Performing minor repairs may require removal from the vehicle/machine. Thoroughly clean the unit before beginning maintenance or repair activities. Since dirt and contamination are the greatest enemies of any type of hydraulic equipment, follow cleanliness requirements strictly. This is especially important when changing the system filter and when removing hoses or plumbing.

A worldwide network of Danfoss Authorized Service Centers is available for major repairs. Danfoss trains and certifies Authorized Service Centers on a regular basis. You can locate your nearest Authorized Service Center using the distributor locator at www.sauer-danfoss.com.

Warranty

Performing installation, maintenance, and minor repairs according to the procedures in this manual will not affect your warranty. Major repairs requiring the removal of the units center section voids the warranty unless completed by a Danfoss Global Service Partner.

General Instructions

Follow these general procedures.

Remove the unit

Prior to performing major repairs, remove the unit from the vehicle/machine. Chock the wheels on the vehicle or lock the mechanism to inhibit movement. Be aware that hydraulic fluid may be under high pressure and/or hot. Inspect the outside of the HST and fittings for damage. Cap hoses and plug ports after removal to prevent contamination.

Keep it clean

Cleanliness is a primary means of assuring satisfactory HST life, on either new or repaired units. Clean the outside of the HST thoroughly before disassembly. Take care to avoid contamination of the system ports. Cleaning parts using a clean solvent wash and air drying is usually adequate.

As with any precision equipment, keep all parts free of foreign materials and chemicals. Protect all exposed sealing surfaces and open cavities from damage and foreign material. If left unattended, cover the transmission with a protective layer of plastic.

Lubricate moving parts

During assembly, coat all moving parts with clean hydraulic fluid. This assures that these parts are lubricated during start-up.

Replace all O-rings and gaskets

Danfoss recommends you replace all O-rings, seals, and gaskets during repair.Lightly lubricate all O-rings with clean petroleum jelly prior to assembly. Grease must be soluable in hydraulic fluid.

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Service Manual

LDU20/24 Closed Circuit Axial Piston Transmission

Introduction

Secure the unit

For major repair, place the unit in a stable position with the shaft pointing downward. It is necessary to secure the transmission while removing and torquing components and fasteners.

Safety Precautions

Always consider safety precautions before beginning a service procedure. Protect yourself and others from injury. Take the following general precautions whenever servicing a hydraulic system.

Unintended machine movement

W Warning

Unintended movement of the machine or mechanism may cause injury to the technician or bystanders. To protect against unintended movement, secure the machine or disable/disconnect the mechanism while servicing.

Flammable cleaning solvents

W Warning

Some cleaning solvents are flammable. To avoid possible fire, do not use cleaning solvents in an area where a source of ignition may be present.

Fluid under pressure

W Warning

Escaping hydraulic fluid under pressure can have sufficient force to penetrate your skin causing serious injury and/or infection. This fluid may also be hot enough to cause burns. Use caution when dealing with hydraulic fluid under pressure. Relieve pressure in the system before removing hoses, fittings, gauges, or components. Never use your hand or any other body part to check for leaks in a pressurized line. Seek medical attention immediately if you are cut by hydraulic fluid.

Personal safety

W Warning

Protect yourself from injury. Use proper safety equipment, including safety glasses, at all times.

Hazardous material

W Warning

Hydraulic fluid contains hazardous material. Avoid prolonged contact with hydraulic fluid. Always dispose of used hydraulic fluid according to environmental regulations.

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Service Manual

LDU20/24 Closed Circuit Axial Piston Transmission

Introduction

Symbols Used in Danfoss Literature

WARNING may result in injury

CAUTION may result in damage to product or property

Non-reusable part, use a new part

External hex head

Internal hex head

Lubricate with hydraulic fluid

Apply grease / petroleum jelly

Inspect for wear or damage

Clean area or part

Be careful not to scratch or damage

Note correct orientation

Torque specification

Press in – press fit

Measurement required

Pull out with tool – press fit

Flatness specification

Parallelism specification

Cover splines with installation cylinder

Mark orientation for reinstallation

The symbols above appear in the illustrations and text of this manual. They are intended to communicate helpful information at the point where it is most useful to the reader. In most instances, the appearance of the symbol itself denotes its meaning. The legend above defines each symbol and explains its purpose.

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Service Manual

LDU20/24 Closed Circuit Axial Piston Transmission

General Description

Basic Design

LDU20/24 is a U-style HST transmission, 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 machine & Compact Utility Tractor of up to 26kw[35PS]

•Compact design

•U-style layout in One housing with Z-shaft configuration

•Available external charge

•Bypass valve for the pulling of the vehicle

•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 capability in most compact design in this class of HST

•Low 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		MA2

MB1		MB2
L1	L2	P400004

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