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Design Closed Circuit

Introduction, May 2012

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Main Menu

Basic Hydrostatic (closed circuit)

System Overview

Functionality of

components

Hydraulic Fluids

Filtration Reservoir Heat Exchanger

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Main Menu

Basic Hydrostatic (closed circuit)

System Overview

Functionality of

components

Hydraulic Fluids

Filtration Reservoir Heat Exchanger

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1. System OverviewHydrostatic Transmission• Continuously variable speed w/o loss of traction

A

BSpeed [km/h]

Tra

cti v

e F

orc e

[N]

Pump Ratio Motor Ratio

Installed Engine Power

hydrostatic transmission

- source 1 -

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1. System OverviewHydrostatic Transmission

• Motor output torque and speed depends on pump and motor displacement

• Speed of hydrostatic transmission is reciprocal to displacements

• Torque is proportional to displacements

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Main Menu

Basic Hydrostatic (closed circuit)

System Overview

Functionality of

components

Hydraulic Fluids

Filtration Reservoir Heat Exchanger

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2. Functionality of ComponentsIntegrated Charge Pump

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2. Functionality of Components Integrated Charge Pump • Charge pump is a fixed displacement pump (gerotor-type)

which is directly connected to the pump input shaft

• Charge pump displacement should be sized to approximately 10% of whole system displacement (pump and motor(s) displacements) in most applications

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2. Functionality of Components Charge Pump - Functions

Charge Pump flow rate functions:• Replenish leakage oil of pump and motor• Replenish loop flushing oil through the flushing valve• Provide flow for the servo control systems• Provide flow for auxiliary circuit functions e.g. parking brake

release

Charge Pump pressure functions: • Maintain low loop pressure• Provide sufficient pressure to activate the servo control

systems

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2. Functionality of ComponentsCharge Pressure Relief Valve

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2. Functionality of Components Charge Pressure Relief Valve• Charge pressure relief valve is necessary

to maintain low loop pressure• Protects the charge pump by limiting the

charge pressure• Excess charge pump output flow is

directed into the pump case

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2. Functionality of ComponentsCharge Check Valve

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2. Functionality of Components Charge Check Valve• It protects the charge pressure system

(charge pump), otherwise a backflow from high pressure side will damaged the charge pump

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2. Functionality of ComponentsLoop Flushing System

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2. Functionality of ComponentsLoop Flushing System• Loop Flushing is necessary because of cooling

requirements and contamination removal of system circuit

• The LF-system removes fluid from the low pressure side of the closed circuit system

• Loop Flushing valves are available with different flow rates to optimize flush flow requirements in all system operating conditions

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2. Functionality of ComponentsHigh Pressure Relief Valve (HPRV)

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2. Functionality of ComponentsHigh Pressure Relief Valve (HPRV)• High pressure relief valves are needed in hydrostatic

transmission systems to limit maximum pressures– Pressures above the product ratings will damage the

transmission– HPRV protect pumps, motors, hoses and other system

components

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2. Functionality of Components Pressure Limiter• Pressure Limiter is a non dissipative high pressure

control

• Limits the heat generated in the system when pressures are too high

• PL changes the displacement of the pump in response to high system pressure

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2. Functionality of Components Bypass• Bypass function allows an internal connection to be

made between the two loops in the hydrostatic transmission

• Function allows the vehicle to be moved without the engine running– Allows for disabled vehicles to be loaded onto a trailer or moved

off the road– Intended to be for slow, short durations otherwise the

hydrostatic transmission can be damaged

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Main Menu

Basic Hydrostatic (closed circuit)

System Overview

Functionality of

components

Hydraulic Fluids

Filtration Reservoir Heat Exchanger

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3. Hydraulic FluidsWhat do you know about Hydraulic Fluids?

Dirt

Blood

SunWaterAir

Alcohol

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3. Hydraulic FluidsOverview Hydraulic Fluid Groups

1. Mineral oil based hydraulic fluids

2. Biogradeable hydraulic fluids• Syntetic ester (HEES) • Rape oil alkaline (HETG)

3. Fire resistance fluids• ATEX Regulation

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3. Hydraulic FluidsRecommended Hydraulic Fluids• Find recommended Hydraulic Fluids for Sauer-Danfoss

hydrostatic components in Technical Literature*

• Fluids meeting the technical literature requirements will very likely provide acceptable unit life

• field testing is the only truly indication of fluid performance

• Sauer-Danfoss warranty claim policies do not apply for fluid related damage

*: “Hydraulic Fluids and Lubricants Technical Information”; page 20

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3. Hydraulic FluidsPhysical Behavior

1. Viscosity• Viscosity grade (VG)• Depends on temperature and pressure• Compromise between flow losses and leakage

2. Density• Depends on temperature and pressure

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3. Hydraulic FluidsPhysical Behavior

Temperature-Behavior Pressure-Behaviour

Temperature Temperature

kine

mat

ic Vi

scos

ity

kine

mat

ic Vi

scos

ity

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3. Hydraulic FluidsViskosity and Temerature Limits• Viscosity and temperature limits in the table “Viscosity and

temperature limits” in technical information* are to be observed

• Under normal operating condition it is recommended to keep the temperature in the range of 30 °C to 60 °C

• Rule of thumb: fluid temperature increase from 80 °C [176 °F] to 90 °C [194 °F] may reduce fluid life by 50 %

*: “Hydraulic Fluids and Lubricants Technical Information”; page 19

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3. Hydraulic FluidsAdditives

Improvement of oil attributes • Viscosity-temperature behavior• Wear protection• Corrosion protection• Ageing resistance• Foam prevention• Bond to dirt particles

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3. Hydraulic FluidsSelection Criteria• Manufacturer‘s instructions

• Release of diverse oils

• Depends on system• Application (vehicle, temperature conditions) • Fill rate

• Application environment• Climate• Area of application (i.e. environmental, flammability regulations, etc.)

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3. Hydraulic FluidsAdditional Information• Technical Information “Hydraulic Fluids and Lubricants”

(520L0463)• Technical Information “Experience with Biodegradable

Hydraulic Fluids” (520L0465)

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Main Menu

Basic Hydrostatic (closed circuit)

System Overview

Functionality of

components

Hydraulic Fluids

Filtration Reservoir Heat Exchanger

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4. FiltrationContamination

Sources of contamination:– Installation– System components– Fill oil– Repair of a unit

Types of contamination:– Metal– Synthetic materials– Organic materials– Plastic– Water– Etc.

Scratches on Piston Shoe

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4. Filtration Cleanliness ClassesISO 4406 1999:• Specification of three cleanliness

classes correlated to particle size ≥4; ≥6; ≥14 [μm]

• Example:ISO 18/16/13

number of particles 1/ml

cleanliness classes (ISO 4406)

0,01-0,02 10,02-0,04 20,04-0,08 30,08-0,16 40,16-0,32 50,32-0,64 6

etc. etc.40-80 1380-160 14160-320 15320-640 16

640-1300 171300-2500 182500-5000 19

5000-10000 2010000-20000 2120000-40000 2240000-80000 2380000-160000 24

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4. Filtration Cleanliness ClassesSauer-Danfoss recommends the cleanliness classes below for different applications*

Product Required cleenliness class ISO 4406-1999

Steering components with open center 22/20/17Orbital motors 22/20/16Steering components with LS and closed center

21/19/16Proportional spool valvesAxial + radial piston pumps and motors

22/18/13Gear pumps and motorsCartridge and electrohydraulic valves 18/16/13

Maximum class at machine start up 25/22/17

*: “Design Guideline for Hydraulic Fluid Cleanliness Technical Information” (520L0467), p. 13, Spreadsheet: “Fluid cleanliness requirements according to product“

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4. Filtration Kind of FiltrationPartial flow filtration

+ Small filter- Partial backflow of oil w/o filtration - Charge pump unprotected (pre-filtration

necessary)

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4. Filtration Kind of FiltrationFull flow filtration

+ Complete oil filtration + Small filter- Charge pump unprotected ( pre-filtration necessary)

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4. Filtration Kind of FiltrationSuction filtration

+ Charge pump protected- Large filter surface necessary- Disadvantageous at low temperature

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Main Menu

Basic Hydrostatic (closed circuit)

System Overview

Functionality of

components

Hydraulic Fluids

Filtration Reservoir Heat Exchanger

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5. ReservoirOverviewArt der FilterungTasks:• Fluid reservoir

• Ensures there is enough oil for hydraulic system

• Cooling

• Separates dirt, water and air

• Assures smooth fluid flow (laminar flow) at suction

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Main Menu

Basic Hydrostatic (closed circuit)

System Overview

Functionality of

components

Hydraulic Fluids

Filtration Reservoir Heat Exchanger

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6. Heat ExchangerFunction and TypeRemoval of hydraulic-system heat

• Prevents overheating of oil• Ideal oil-temperature should be 60 to 80°C

Construction type in mobile hydraulic• Oil-air-heat exchanger

Oil-air heat exchanger

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6. Heat ExchangerDesign Criteria

vehicle engine cooler fan SD FD system

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6. Heat ExchangerSauer-Danfoss Fan Driveexample: closed circuit

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The EndMENU

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Many Thanks for YOUR Attention!

When Chuck Norris says “420 bar" he is not quoting the pressure rating of the H1B motor, he is telling you how much pressure his foot will apply to your face.

The three things that make hydraulics work:1. Flow2. Pressure3. Chuck Norris

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Overview Literature SourcesMENU

- Source 1 - Ölhydraulik – Handbuch für die hydrostatisch Leistungsübertragung in der

Fluidtechnik; Findeisen, D.; Springer