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Application Notes

Lift Trucks

Fluid Power in Motion

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2/6EATON F(x) Software and Electronics E-ELCL-MR001-E April 20072

Solutions

for Lift Trucks.

EATON Lift Trucks E-HYOV-MR004-E September 20072

Eaton has the products and capabilities to provide completesystem solutions for your application needs. World class

hydraulic components, electronic controllers and software arejust part of the value Eaton brings to make your applications

deliver the power, in fluid power. Tough applications requirethe experience and knowledge that Eaton can provideand this application information will help you get started.

Contact your Eaton representative for further information orvisit us on-line at www.hydraulics.eaton.com.

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Forklift TruckApplications

The standard forklift, alsocommonly known as acounterbalanced sit-downlift truck, is the vehicle mostpeople think of when theythink Lift truck or Forklifttruck. They are available insmaller sizes with batteryoperation but the majorityare run from several differentfuel types especially as thevehicle gets larger and thelift capacity increases. Thereis quite a range of weightcapacities, lift heights, andattachment options availablein the market, many with

their own special needsfrom the hydraulic systemin order to provide smoothreliable operation whenhandling various types andsizes of loads. The systemrequirements will be differentfor a smaller lift truck witha low lift height versus amachine pushing 40 tonslift capacity or one with asignificant lift height capability.

The lift capacity of a truck isaffected not only by the load,

but also by the lift heightand the physical size of theload. A larger size load movesthe center of gravity of theload further from the wheelseffectively reducing the liftcapacity as does the heightthe load is being lifted. Thelift truck mass and centerof gravity determines themaximum lift capacity andhow far from the mast agiven load center can belocated and still provide astable platform. Caution mustbe used in selecting the lifttruck system components

and attachments since theload and the load centermust be determined underall operating conditions toensure that the truck is stable.This same caution applies toany hydraulic controls usedto operate the mast or tilt ona typical forklift truck. Withlow lift heights centeredclose to the mast a simpleon-off control valve can beused. This simple inexpensiveapproach is often seenon small electric powered

trucks. As the load capacityincreases, or the load centeris further from the truck mast,or the lift height is increased,the precision of the hydraulicsmust be improved. Anysudden movement caused byan on-off valve with a heavyload high in the air can bevery uncomfortable to theoperator and also potentiallycause the truck to tip becauseof a high inertia load extendedso far out in the air. Smooth,controllable operation isabsolutely necessary asheavier loads and higher

lift heights are utilized. Thesame can be said for thepropel circuit. If a heavy loadmust be inched into locationat some significant heightthe operator must have thecapability to smoothly inch themachine without jerking theload.

Many types of hydraulicpropel circuits have beenused over the years. Theycan range from a simple gearpump and Low Speed High

Torque (LSHT) motor circuitwith a valve controlling thedirection and speed of travel,to complete closed loophydrostatic transmissions withvariable displacement pistonpumps and fixed or variabledisplacement motors. Usinghigh-speed piston motors forpropel will require the useof a gearbox to provide thenecessary gear reductionand output shaft bearings tosupport the weight of themachine. This design providesvery smooth operation andhigh efficiencies, but comes

at a cost penalty. Where thedisplacement and loadingconditions permit, the use ofGeroler type low speed hightorque motors can providea compact, cost effectivedrive motor and, in manycases, without the need for agearbox.

Hydraulic steering systemscan range from open centersystems to closed center loadsensing systems, and todaysteer by wire is also being

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actively investigated. Withthe availability of two speedsteering units and options likeEatons Q-amp, almost anydesired steering characteristiccan be provided today. At lowsteering speeds the steeringis slow to provide preciseposition control, but whenmaking sharp turns rapidly thespeed of the steering is spedup to provide rapid responseand limit the number of turnsthat the operator has to applyto the steering wheel.

There are a lot of options andfeatures available within thesteering offerings today andcareful consideration shouldbe given to the compromisesin order to provide thebest operator comfort andproductivity. Most of thesteering systems appliedtoday do not synchronize thesteering wheel to the actualsteering angle on the wheels,but systems are available thatcan give the same feedbackand feel as your car. If it is

desired to have the steeringwheel return to the sameposition as in your car, thenthe Eaton EPACS steeringcontrol system should beinvestigated. There arecertain markets in the worldwhere this type of systemhas become the standard.

Control valves for lift truckscan be a simple open centervalve, closed center, or closedcenter with flow and loadsensing. Operation can beby a manual lever, remotehydraulic operation, or electro-hydraulic with either simpleon-off operation or completeproportional control, or anycombination of these. Oneimportant factor is to considerthe load holding requirements,especially with so manydifferent attachments utilizedwith lift trucks. Typically onthe smaller trucks, only aspool valve might be used forholding the load from driftingdown. A counter-balancevalve or tilt-lock load holding

valve is typically used for thetilt function. This preventsthe tilt function from beinginadvertently operated if theengine is off and the load wasleft up, thereby preventing aload from sliding off the forks.Certain markets may demanda flow control valve to limitthe maximum lowering speedor a counterbalance valve toprecisely control the loweringvelocity.

Today, with the advent ofnumerous reliable electro-hydraulic components andcontrols options available,there is a noticeable shiftto using more electro-hydraulics in forklift trucksystems. Electronic controlsprovide numerous benefits inimproving the operation of themachine. A lot of functionscan be easily automatedor semi-automated. If thevehicle is inching to placea load at the same timean operator is asking formaximum lift speed, the

electronics can make thedecision to up the enginespeed, maintain a low pumdisplacement for the propeland provide maximum liftspeed without the operatorneeding to handle multiplecontrols simultaneously.Power management andautomotive drive control isreadily available with ourelectronic control systems.This significantly increasesoperator comfort andproductivity. Electronics alsmakes the addition of loadmonitoring and restricting

the operating envelope of thmachine possible reducing topportunity for the operatorto pick up or position a heavload beyond the machinesdesign capabilities. It isalso possible to completelyautomate the machinefunction for densely packedwarehousing applications.

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HydraulicFunctions

Basic formulae for sizing*

Pump Output Flow (GPM) = RPM x Displ (cid) / 231

(LPM) = RPM x Displ (cc) / 1000

Pump Input Power (HP) = GPM x PSI / (OAL Eff x 1714)

(KW) = LPM x BAR/(OAL Eff x 600)

Hydraulic Motor Speed(RPM) = GPM x 231 x Vol Eff /Disp (cid)

(RPM) = LPM x 1000 x Vol Eff /Disp (cc)

Hydraulic Motor Torque(in-lb) = PSI x Displ (cid) x Mech Eff / (2p)

(N-m) = BAR x Displ (cc) x Mech Eff / (20p)

Cylinder Force (lbs) = Area (in2) x PSI

(N) = Area (mm2) x BAR x 10

Cylinder Speed (in/min) = GPM x 231 / Area (in2)

(mm/min) = LPM x 1000 /Area (mm2)

Steering unit disp (cid/rev) = Cyl Vol (cubic inches) /Number of Revs

(cc/rev) = Cyl Vol (cc) / Number of Revs

Vehicle Ground Speed(MPH) = RPM x 60 x Tire Radius (ft) x PI /

5280

(KPH) = RPM x 60 x Tire Radius (m) x PI /1000

Functions typically drivenand operated by the hydraulicsystem:

Steering

Ground drive / propel

Mast lift

Mast tilt

Mast lift and tilt load holding

Auxiliary attachment controls

Cooling fan drive on largersystems

System design considerations

Review all applicablestandards

Define operating envelope

Evaluate performance / costcompromises

Select and properly size allcomponents

Evaluate ergonomics

Product families typicallyused for hydraulic systems

Open loop steeringcontrol unit

Closed loop steeringcontrol unit

Medium or heavy dutyclosed loop piston pump

Medium or heavy dutyclosed loop piston motor

Open loop piston pump

Open loop gear pump

Open loop disc valve motor

Open loop VIS motor

Open loop spool valve motor

Open center directionalcontrol valve

Flow and load sensingdirectional control valve

Cartridge valves

Cartridge valve manifoldassembly

Filtration

Oil cooler

Fluid conveyance

* The following calculations mayalso need to be considered withregards to sizing:

Basic formulae are general innature and do not take intoaccount efficiency losses forindividual components.

Cylinder pressures andspeeds for mast lift, tilt,and aux., functions

Torque and displacementcalculations for propel loop

Gradeability and travel speedcalculations

Over speed calculation

System Hp calculations underall operating conditions

Power range calculation

Mechanical and volumetricefficiencies

Product life

Cooling capacity

System pressure dropcalculations

Line flow velocity calculations

Electric Trucks -Four Wheel

IC Trucks -Hydrostatic Propel

Typical Circuits

LSGearPump

ElectricMotor

LSCF

EF

LS

PriorityValve

BrakeValveMast

Valve

MastCylinders

SCU w/RMSS

Motion SignalBrake Cylinder

M

Steer Cylinder

Engine

VehicleControlSystem

Steer Cylinder

PumpHD/MD

GearPump

PriorityValve

LS

LS

CF

EFBrakeValveMast

Valve

MastCylinders

SCU

VIS Motor VIS Motor

Brake Cylinder

Pump Control Output

Engine Control Output

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EatonHydraulics Operations USA14615 Lone Oak Road

Eden Prairie, MN 55344

USA

Tel: 952-937-9800

Fax: 952-294-7722

www.hydraulics.eaton.com

EatonHydraulics Operations EuropeRoute de la Longeraie 7

1110 Morges

Switzerland

Tel: +41 (0) 21 811 4600

Fax: +41 (0) 21 811 4601

EatonHydraulics Operations Asia Pacific11th Floor Hong Kong New World Tower

300 Huaihai Zhong Road

Shanghai 200021

China

Tel: 86-21-6387-9988

Fax: 86-21-6335-3912

2007 Eaton CorporationAll Rights ReservedPrinted USADocument No. E-HYOV-MR004-ESeptember 2007